pgmoneta

Developer Guide
pgmoneta

Contents

1 Introduction 5
1.1 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2 Platforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2 Installation 7
2.1 Fedora . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2 RHEL 9 / RockyLinux 9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.3 Compiling the source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.3.1 RHEL / RockyLinux . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.3.2 FreeBSD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.3.3 Build . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.4 Compiling the documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.4.1 Build . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.5 Extension installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.5.1 Install pgmoneta_ext . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.5.2 Verify success . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.5.3 Granting SUPERUSER Privileges . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3 C programming 13
3.1 Debugging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4 Git guide 13
4.1 Basic steps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.1.1 Start by forking the repository . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.2 Clone your repository locally . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.2.1 Add upstream . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.2.2 Do a work branch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.2.3 Make the changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.2.4 Multiple commits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.2.5 Rebase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.2.6 Force push . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.2.7 Format source code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.2.8 Repeat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.2.9 Undo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

5 Architecture 16
5.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

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5.2 Shared memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

5.3 Network and messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.4 Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
5.5 Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
5.5.1 Write . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
5.5.2 Read . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5.5.3 Remote management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5.6 libev usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
5.7 Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
5.8 Reload . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
5.9 Prometheus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
5.10 Logging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
5.11 Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

6 Encryption 21
6.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
6.2 Encryption Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
6.3 Encryption / Decryption CLI Commands . . . . . . . . . . . . . . . . . . . . . . . . . 21
6.3.1 decrypt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
6.3.2 encrypt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
6.4 Benchmark . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

7 RPM 26
7.1 Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
7.2 Setup RPM development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
7.3 Create source package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
7.4 Create RPM package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

8 Test 27
8.1 Container Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
8.1.1 Docker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
8.1.2 Podman . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
8.2 Test suite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

9 WAL Reader 29
9.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
9.2 pgmoneta-walinfo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
9.3 High-Level API Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
9.3.1 Struct walfile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

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9.3.2 Function Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

9.4 Internal API Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
9.4.1 parse_wal_file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
9.4.2 Usage Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
9.4.3 WAL File Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
9.5 Resource Managers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
9.5.1 Resource Manager Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
9.5.2 Resource Manager Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
9.5.3 Supporting Various WAL Structures in PostgreSQL Versions 13 to 17 . . . . . . 34
9.6 WAL Change List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
9.6.1 xl_clog_truncate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
9.6.2 xl_commit_ts_truncate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
9.6.3 xl_heap_prune . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
9.6.4 xlhp_freeze_plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
9.6.5 spgxlogState . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
9.6.6 xl_end_of_recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
9.6.7 gingxlogSplit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
9.6.8 gistxlogDelete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
9.6.9 gistxlogPageReuse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
9.6.10 xl_hash_vacuum_one_page . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
9.6.11 xl_heap_prune . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
9.6.12 xl_heap_freeze_plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
9.6.13 xl_heap_freeze_page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
9.6.14 xl_btree_reuse_page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
9.6.15 xl_btree_delete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
9.6.16 spgxlogVacuumRedirect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
9.6.17 xl_xact_prepare . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
9.6.18 xl_xact_parsed_commit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
9.6.19 xl_xact_parsed_abort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
9.6.20 xlogrecord.h flags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
9.6.21 xl_heap_prune . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
9.6.22 xl_heap_vacuum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
9.6.23 xl_btree_metadata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
9.6.24 xl_btree_reuse_page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
9.6.25 xl_btree_delete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
9.6.26 xl_btree_unlink_page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
9.7 Additional Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

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10 Troubleshooting 54
10.1 Could not get version for server . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

11 Acknowledgement 55
11.1 Authors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
11.2 Committers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
11.3 Contributing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

12 License 57
12.1 libart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

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1 Introduction

pgmoneta is a backup / restore solution for PostgreSQL.

Ideally, you would not need to do backups and disaster recovery, but that isn’t how the real World
works.

Possible scenarios that could happen

• Data corruption
• System failure
• Human error
• Natural disaster

and then it is up to the database administrator to get the database system back on-line, and to the
correct recovery point.

Two key factors are

• Recovery Point Objective (RPO): Maximum targeted period in which data might be lost from an
IT service due to a major incident
• Recovery Time Objective (RTO): The targeted duration of time and a service level within which a
business process must be restored after a disaster (or disruption) in order to avoid unacceptable
consequences associated with a break in business continuity

You would like to have both of these as close to zero as possible, since RPO of 0 means that you won’t
lose data, and RTO of 0 means that your system recovers at once. However, that is easier said than
done.

pgmoneta is focused on having features that will allow database systems to get as close to these goals
as possible such that high availability of 99.99% or more can be implemented, and monitored through
standard tools.

pgmoneta is named after the Roman Goddess of Memory.

1.1 Features

• Full backup
• Restore
• Compression (gzip, zstd, lz4, bzip2)
• AES encryption support
• Symlink support
• WAL shipping support

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• Hot standby
• Prometheus support
• Remote management
• Offline mode
• Transport Layer Security (TLS) v1.2+ support
• Daemon mode
• User vault

1.2 Platforms

The supported platforms are

• Fedora 38+
• RHEL 9
• RockyLinux 9
• FreeBSD
• OpenBSD

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2 Installation

2.1 Fedora

You need to add the PostgreSQL YUM repository, for example for Fedora 40

dnf install -y https://download.postgresql.org/pub/repos/yum/reporpms/F

-40-x86_64/pgdg-fedora-repo-latest.noarch.rpm

and do the install via

dnf install -y pgmoneta

Additional information

• PostgreSQL YUM
• Linux downloads

2.2 RHEL 9 / RockyLinux 9

x86_64

dnf install -y https://dl.fedoraproject.org/pub/epel/epel-release-latest

-9.noarch.rpm
dnf install -y https://download.postgresql.org/pub/repos/yum/reporpms/EL
-9-x86_64/pgdg-redhat-repo-latest.noarch.rpm

aarch64

dnf install -y https://dl.fedoraproject.org/pub/epel/epel-release-latest

-9.noarch.rpm
dnf install -y https://download.postgresql.org/pub/repos/yum/reporpms/EL
-9-aarch64/pgdg-redhat-repo-latest.noarch.rpm

and do the install via

dnf install -y pgmoneta

2.3 Compiling the source

We recommend using Fedora to test and run pgmoneta, but other Linux systems, FreeBSD and MacOS
are also supported.

pgmoneta requires

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• clang
• cmake
• make
• libev
• OpenSSL
• zlib
• zstd
• lz4
• bzip2
• systemd
• rst2man
• libssh
• libcurl
• libarchive

dnf install git gcc clang clang-analyzer cmake make libev libev-devel \
openssl openssl-devel \
systemd systemd-devel zlib zlib-devel \
libzstd libzstd-devel \
lz4 lz4-devel libssh libssh-devel \
libcurl libcurl-devel \
python3-docutils libatomic \
bzip2 bzip2-devel \
libarchive libarchive-devel

Alternative gcc can be used.

2.3.1 RHEL / RockyLinux

On RHEL / Rocky, before you install the required packages some additional repositories need to be
enabled or installed first.

First you need to install the subscription-manager

dnf install subscription-manager

It is ok to disregard the registration and subscription warning.

Otherwise, if you have a Red Hat corporate account (you need to specify the company/organization
name in your account), you can register using

subscription-manager register --username <your-account-email-or-login> --

password <your-password> --auto-attach

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Then install the EPEL repository,

dnf install epel-release

Then to enable powertools

dnf config-manager --set-enabled codeready-builder-for-rhel-9-rhui-rpms

dnf config-manager --set-enabled crb
dnf install https://dl.fedoraproject.org/pub/epel/epel-release-latest-9.
noarch.rpm

Then use the dnf command for pgmoneta to install the required packages.

2.3.2 FreeBSD

On FreeBSD, pkg is used instead of dnf or yum.

Use pkg install <package name> to install the following packages

git gcc cmake libev openssl libssh zlib-ng zstd liblz4 bzip2 curl \
py39-docutils libarchive

2.3.3 Build

2.3.3.1 Release build The following commands will install pgmoneta in the /usr/local hierar-
chy.

git clone https://github.com/pgmoneta/pgmoneta.git

cd pgmoneta
mkdir build
cd build
cmake -DCMAKE_INSTALL_PREFIX=/usr/local ..
make
sudo make install

See RPM for how to build a RPM of pgmoneta.

2.3.3.2 Debug build The following commands will create a DEBUG version of pgmoneta.

git clone https://github.com/pgmoneta/pgmoneta.git

cd pgmoneta
mkdir build
cd build
cmake -DCMAKE_C_COMPILER=clang -DCMAKE_BUILD_TYPE=Debug ..
make

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2.4 Compiling the documentation

pgmoneta’s documentation requires

• pandoc
• texlive

dnf install pandoc texlive-scheme-basic \

’tex(footnote.sty)’ ’tex(footnotebackref.sty)’ \
’tex(pagecolor.sty)’ ’tex(hardwrap.sty)’ \
’tex(mdframed.sty)’ ’tex(sourcesanspro.sty)’ \
’tex(ly1enc.def)’ ’tex(sourcecodepro.sty)’ \
’tex(titling.sty)’ ’tex(csquotes.sty)’ \
’tex(zref-abspage.sty)’ ’tex(needspace.sty)’

You will need the Eisvogel template as well which you can install through

wget https://github.com/Wandmalfarbe/pandoc-latex-template/releases/
download/2.4.2/Eisvogel-2.4.2.tar.gz
tar -xzf Eisvogel-2.4.2.tar.gz
mkdir -p $HOME/.local/share/pandoc/templates
mv eisvogel.latex $HOME/.local/share/pandoc/templates

where $HOME is your home directory.

2.4.0.1 Generate API guide This process is optional. If you choose not to generate the API HTML
files, you can opt out of downloading these dependencies, and the process will automatically skip the
generation.

Download dependencies

dnf install graphviz doxygen

2.4.1 Build

These packages will be detected during cmake and built as part of the main build.

2.5 Extension installation

When you configure the extra parameter in the server section of pgmoneta.conf, it requires the
server side to have the pgmoneta_ext extension installed to make it work.

The following instructions can help you easily install pgmoneta_ext. If you encounter any problems,
please refer to the more detailed instructions in the DEVELOPERS documentation.

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2.5.1 Install pgmoneta_ext

After you have successfully installed pgmoneta, the following commands will help you install
pgmoneta_ext:

dnf install -y pgmoneta_ext

You need to add the pgmoneta_ext library for PostgreSQL in postgrersql.conf as well:

shared_preload_libraries = ’pgmoneta_ext’

And remember to restart PostgreSQL to make it work.

2.5.2 Verify success

You can use the postgres role to test.

1. Log into PostgreSQL

psql

2. Create a new test database

CREATE DATABASE testdb;

3. Enter the database

\c testdb

4. Follow the SQL commands below to check the function

DROP EXTENSION IF EXISTS pgmoneta_ext;

CREATE EXTENSION pgmoneta_ext;
SELECT pgmoneta_ext_version();

You should see

pgmoneta_ext_version
----------------------
0.1.0
(1 row)

2.5.3 Granting SUPERUSER Privileges

Some functions in pgmoneta_ext require SUPERUSER privileges. To enable these, grant the repl
role superuser privileges using the command below. Please proceed with caution: granting superuser

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privileges bypasses all permission checks, allowing unrestricted access to the database, which can
pose security risks. We are committed to enhancing privilege security in future updates.

ALTER ROLE repl WITH SUPERUSER;

To revoke superuser privileges from the repl role, use the following command:

ALTER ROLE repl WITH NOSUPERUSER;

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3 C programming

pgmoneta is developed using the C programming language so it is a good idea to have some knowledge
about the language before you begin to make changes.

There are books like,

• C in a Nutshell
• 21st Century C

that can help you

3.1 Debugging

In order to debug problems in your code you can use gdb, or add extra logging using the
pgmoneta_log_XYZ() API

4 Git guide

Here are some links that will help you

• How to Squash Commits in Git

• ProGit book

4.1 Basic steps

4.1.1 Start by forking the repository

This is done by the “Fork” button on GitHub.

4.2 Clone your repository locally

This is done by

git clone git@github.com:<username>/pgmoneta.git

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4.2.1 Add upstream

Do

cd pgmoneta
git remote add upstream https://github.com/pgmoneta/pgmoneta.git

4.2.2 Do a work branch

git checkout -b mywork main

4.2.3 Make the changes

Remember to verify the compile and execution of the code.

Use

[#xyz] Description

as the commit message where [#xyz] is the issue number for the work, and Description is a
short description of the issue in the first line

4.2.4 Multiple commits

If you have multiple commits on your branch then squash them

git rebase -i HEAD~2

for example. It is p for the first one, then s for the rest

4.2.5 Rebase

Always rebase

git fetch upstream

git rebase -i upstream/main

4.2.6 Force push

When you are done with your changes force push your branch

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git push -f origin mywork

and then create a pull request for it

4.2.7 Format source code

Use

./uncrustify.sh

to format the source code

4.2.8 Repeat

Based on feedback keep making changes, squashing, rebasing and force pushing

4.2.9 Undo

Normally you can reset to an earlier commit using git reset <commit hash> --hard.

But if you accidentally squashed two or more commits, and you want to undo that, you need to know
where to reset to, and the commit seems to have lost after you rebased.

But they are not actually lost - using git reflog, you can find every commit the HEAD pointer has
ever pointed to. Find the commit you want to reset to, and do git reset --hard.

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5 Architecture

5.1 Overview

pgmoneta use a process model (fork()), where each process handles one Write-Ahead Log (WAL)
receiver to PostgreSQL.

The main process is defined in main.c.

Backup is handled in backup.h (backup.c).

Restore is handled in restore.h (restore.c) with linking handled in link.h (link.c).

Archive is handled in achv.h (archive.c) backed by restore.

Write-Ahead Log is handled in wal.h (wal.c).

Backup information is handled in info.h (info.c).

Retention is handled in retention.h (retention.c).

Compression is handled in gzip_compression.h (gzip_compression.c), lz4_compression.h

(lz4_compression.c), zstandard_compression.h (zstandard_compression.c), and bzip2_compression.h
(bzip2_compression.c).

Encryption is handled in aes.h (aes.c).

5.2 Shared memory

A memory segment (shmem.h) is shared among all processes which contains the pgmoneta state
containing the configuration and the list of servers.

The configuration of pgmoneta (struct configuration) and the configuration of the servers
(struct server) is initialized in this shared memory segment. These structs are all defined in
pgmoneta.h.

The shared memory segment is created using the mmap() call.

5.3 Network and messages

All communication is abstracted using the struct message data type defined in messge.h.

Reading and writing messages are handled in the message.h (message.c) files.

Network operations are defined in network.h (network.c).

16
pgmoneta

5.4 Memory

Each process uses a fixed memory block for its network communication, which is allocated upon
startup of the process.

That way we don’t have to allocate memory for each network message, and more importantly free it
after end of use.

The memory interface is defined in memory.h (memory.c).

5.5 Management

pgmoneta has a management interface which defines the administrator abilities that can be performed
when it is running. This include for example taking a backup. The pgmoneta-cli program is used
for these operations (cli.c).

The management interface is defined in management.h. The management interface uses its own
protocol which uses JSON as its foundation.

5.5.1 Write

The client sends a single JSON string to the server,

Field Type Description

compression uint8 The compression type

encryption uint8 The encryption type
length uint32 The length of the JSON document
json String The JSON document

The server sends a single JSON string to the client,

Field Type Description

compression uint8 The compression type

encryption uint8 The encryption type
length uint32 The length of the JSON document

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pgmoneta

Field Type Description

json String The JSON document

5.5.2 Read

The server sends a single JSON string to the client,

Field Type Description

compression uint8 The compression type

encryption uint8 The encryption type
length uint32 The length of the JSON document
json String The JSON document

The client sends to the server a single JSON documents,

Field Type Description

compression uint8 The compression type

encryption uint8 The encryption type
length uint32 The length of the JSON document
json String The JSON document

5.5.3 Remote management

The remote management functionality uses the same protocol as the standard management method.

However, before the management packet is sent the client has to authenticate using SCRAM-SHA-256
using the same message format that PostgreSQL uses, e.g. StartupMessage, AuthenticationSASL, Au-
thenticationSASLContinue, AuthenticationSASLFinal and AuthenticationOk. The SSLRequest message
is supported.

The remote management interface is defined in remote.h (remote.c).

18
pgmoneta

5.6 libev usage

libev is used to handle network interactions, which is “activated” upon an EV_READ event.

Each process has its own event loop, such that the process only gets notified when data related only to
that process is ready. The main loop handles the system wide “services” such as idle timeout checks
and so on.

5.7 Signals

The main process of pgmoneta supports the following signals SIGTERM, SIGINT and SIGALRM as a
mechanism for shutting down. The SIGABRT is used to request a core dump (abort()).

The SIGHUP signal will trigger a reload of the configuration.

It should not be needed to use SIGKILL for pgmoneta. Please, consider using SIGABRT instead,
and share the core dump and debug logs with the pgmoneta community.

5.8 Reload

The SIGHUP signal will trigger a reload of the configuration.

However, some configuration settings requires a full restart of pgmoneta in order to take effect. These
are

• hugepage
• libev
• log_path
• log_type
• unix_socket_dir
• pidfile

The configuration can also be reloaded using pgmoneta-cli -c pgmoneta.conf conf

reload. The command is only supported over the local interface, and hence doesn’t work
remotely.

5.9 Prometheus

pgmoneta has support for Prometheus when the metrics port is specified.

The module serves two endpoints

19
pgmoneta

• / - Overview of the functionality (text/html)

• /metrics - The metrics (text/plain)

All other URLs will result in a 403 response.

The metrics endpoint supports Transfer-Encoding: chunked to account for a large amount of
data.

The implementation is done in prometheus.h and prometheus.c.

5.10 Logging

Simple logging implementation based on a atomic_schar lock.

The implementation is done in logging.h and logging.c.

5.11 Protocol

The protocol interactions can be debugged using Wireshark or pgprtdbg.

20
pgmoneta

6 Encryption

6.1 Overview

AES Cipher block chaining (CBC) mode and AES Counter (CTR) mode are supported in pgmoneta. The
default setup is no encryption.

CBC is the most commonly used and considered save mode. Its main drawbacks are that encryption is
sequential (decryption can be parallelized).

Along with CBC, CTR mode is one of two block cipher modes recommended by Niels Ferguson and
Bruce Schneier. Both encryption and decryption are parallelizable.

Longer the key length, safer the encryption. However, with 20% (192 bit) and 40% (256 bit) extra
workload compare to 128 bit.

6.2 Encryption Configuration

none: No encryption (default value)

aes | aes-256 | aes-256-cbc: AES CBC (Cipher Block Chaining) mode with 256 bit key
length

aes-192 | aes-192-cbc: AES CBC mode with 192 bit key length

aes-128 | aes-128-cbc: AES CBC mode with 128 bit key length

aes-256-ctr: AES CTR (Counter) mode with 256 bit key length

aes-192-ctr: AES CTR mode with 192 bit key length

aes-128-ctr: AES CTR mode with 128 bit key length

6.3 Encryption / Decryption CLI Commands

6.3.1 decrypt

Decrypt the file in place, remove encrypted file after successful decryption.

Command

pgmoneta-cli decrypt <file>

21
pgmoneta

6.3.2 encrypt

Encrypt the file in place, remove unencrypted file after successful encryption.

Command

pgmoneta-cli encrypt <file>

6.4 Benchmark

Check if your CPU have AES-NI

cat /proc/cpuinfo | grep aes

Query number of cores on your CPU

lscpu | grep ’^CPU(s):’

By default openssl using AES-NI if the CPU have it.

openssl speed -elapsed -evp aes-128-cbc

Speed test with explicit disabled AES-NI feature

OPENSSL_ia32cap="~0x200000200000000" openssl speed -elapsed -evp aes-128-

cbc

Test decrypt

openssl speed -elapsed -decrypt -evp aes-128-cbc

Speed test with 8 cores

openssl speed -multi 8 -elapsed -evp aes-128-cbc

Architecture: x86_64
CPU op-mode(s): 32-bit, 64-bit
Address sizes: 39 bits physical, 48 bits virtual
Byte Order: Little Endian
CPU(s): 12
On-line CPU(s) list: 0-11
Vendor ID: GenuineIntel
Model name: Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
CPU family: 6
Model: 158
Thread(s) per core: 2
Core(s) per socket: 6
Socket(s): 1

22
pgmoneta

Stepping: 10
BogoMIPS: 5183.98
Flags: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr
pge mca cmov pat pse36 clflush mmx fxsr sse sse2 s
s ht syscall nx pdpe1gb rdtscp lm constant_tsc
rep_good nopl xtopology cpuid pni pclmulqdq
vmx ssse
3 fma cx16 pcid sse4_1 sse4_2 movbe popcnt aes
xsave avx f16c rdrand hypervisor lahf_lm abm 3
dnowpr
efetch invpcid_single pti ssbd ibrs ibpb stibp
tpr_shadow vnmi ept vpid ept_ad fsgsbase bmi1
avx2 s
mep bmi2 erms invpcid rdseed adx smap clflushopt
xsaveopt xsavec xgetbv1 xsaves flush_l1d
arch_capa
bilities
Virtualization features:
Virtualization: VT-x
Hypervisor vendor: Microsoft
Virtualization type: full
Caches (sum of all):
L1d: 192 KiB (6 instances)
L1i: 192 KiB (6 instances)
L2: 1.5 MiB (6 instances)
L3: 12 MiB (1 instance)
Vulnerabilities:
Itlb multihit: KVM: Mitigation: VMX disabled
L1tf: Mitigation; PTE Inversion; VMX conditional cache
flushes, SMT vulnerable
Mds: Vulnerable: Clear CPU buffers attempted, no
microcode; SMT Host state unknown
Meltdown: Mitigation; PTI
Spec store bypass: Mitigation; Speculative Store Bypass disabled via
prctl and seccomp
Spectre v1: Mitigation; usercopy/swapgs barriers and __user
pointer sanitization
Spectre v2: Mitigation; Full generic retpoline, IBPB
conditional, IBRS_FW, STIBP conditional, RSB filling
Srbds: Unknown: Dependent on hypervisor status
Tsx async abort: Not affected

openssl version: 3.0.5

built on: Tue Jul 5 00:00:00 2022 UTC
options: bn(64,64)
compiler: gcc -fPIC -pthread -m64 -Wa,--noexecstack -O2 -flto=auto -ffat-
lto-objects -fexceptions -g -grecord-gcc-switches -pipe -Wall -Werror=
format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -
specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -fstack-protector-strong
-specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -mtune=generic -
fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection -

23
pgmoneta

O2 -flto=auto -ffat-lto-objects -fexceptions -g -grecord-gcc-switches -

pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-
D_GLIBCXX_ASSERTIONS -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -
fstack-protector-strong -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -
m64 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-
protection -fcf-protection -Wa,--noexecstack -Wa,--generate-missing-
build-notes=yes -specs=/usr/lib/rpm/redhat/redhat-hardened-ld -specs=/
usr/lib/rpm/redhat/redhat-annobin-cc1 -DOPENSSL_USE_NODELETE -DL_ENDIAN
-DOPENSSL_PIC -DOPENSSL_BUILDING_OPENSSL -DZLIB -DNDEBUG -DPURIFY -
DDEVRANDOM="\"/dev/urandom\"" -DSYSTEM_CIPHERS_FILE="/etc/crypto-
policies/back-ends/openssl.config"
The ’numbers’ are in 1000s of bytes per second processed.
type 16 bytes 64 bytes 256 bytes 1024 bytes 8192
bytes 16384 bytes
AES-128-CBC * 357381.06k 414960.06k 416301.23k 416687.10k
416175.45k 416268.29k
AES-128-CBC 902160.83k 1496344.68k 1514778.62k 1555236.52k
1542537.22k 1569259.52k
AES-128-CBC d 909710.79k 2941259.46k 5167110.31k 5927086.76k
6365967.70k 6349198.68k
AES-128-CBC 8 3912786.36k 8042348.31k 9870507.86k 10254096.38k
10653332.82k 10310331.05k
AES-128-CBC 8d 4157037.26k 12337480.36k 26613686.27k 29902703.27k
32306793.13k 31440366.25k

AES-128-CTR * 146971.83k 165696.94k 574871.64k 634507.61k

676448.94k 668139.52k
AES-128-CTR 887783.06k 2255074.22k 4800168.19k 5930596.01k
6431110.49k 6376062.98k
AES-128-CTR d 793432.63k 2181439.06k 4541298.09k 5743022.42k
6480090.45k 6271221.76k
AES-128-CTR 8 3833975.47k 10832239.55k 23757293.40k 28413146.79k
30514317.99k 30092356.27k
AES-128-CTR 8d 3456838.44k 9749773.91k 22107652.18k 27229352.28k
30703026.18k 29387025.07k

AES-192-CBC 853380.50k 1238507.90k 1299788.12k 1257189.03k

1272591.70k 1271840.77k
AES-192-CBC d 876094.29k 2843770.82k 4523019.52k 5177496.92k
5442652.84k 5372559.36k
AES-192-CTR 869039.84k 2285946.18k 4229439.91k 5049118.04k
5422994.77k 5309748.57k
AES-192-CTR d 789470.51k 2177050.05k 4194812.76k 4935891.63k
5257865.90k 5323046.91k

AES-256-CBC 834298.24k 1100648.64k 1117826.90k 1104301.40k

1130657.11k 1097285.63k
AES-256-CBC d 843079.68k 2714917.67k 4084088.23k 4510005.59k
4557821.27k 4594783.57k
AES-256-CTR 811325.74k 2222582.89k 3749333.08k 4412143.27k
4640549.55k 4554828.46k

24
pgmoneta

AES-256-CTR d 730844.97k 2081179.20k 3673258.15k 4346793.64k

4515722.58k 4594335.74k

*: AES-NI disabled; 8: 8 cores; d: decryption

25
pgmoneta

7 RPM

pgmoneta can be built into a RPM for Fedora systems.

7.1 Requirements

dnf install gcc rpm-build rpm-devel rpmlint make python bash coreutils
diffutils patch rpmdevtools chrpath

7.2 Setup RPM development

rpmdev-setuptree

7.3 Create source package

git clone https://github.com/pgmoneta/pgmoneta.git

cd pgmoneta
mkdir build
cd build
cmake -DCMAKE_BUILD_TYPE=Release ..
make package_source

7.4 Create RPM package

cp pgmoneta-$VERSION.tar.gz ~/rpmbuild/SOURCES
QA_RPATHS=0x0001 rpmbuild -bb pgmoneta.spec

The resulting RPM will be located in ~/rpmbuild/RPMS/x86_64/, if your architecture is x86_64

.

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pgmoneta

8 Test

8.1 Container Environment

8.1.1 Docker

First, ensure your system is up to date.

dnf update

Install the necessary packages for Docker.

dnf -y install dnf-plugins-core

Add the Docker repository to your system.

sudo dnf config-manager --add-repo https://download.docker.com/linux/

fedora/docker-ce.repo

Install Docker Engine, Docker CLI, and Containerd.

sudo dnf install docker-ce docker-ce-cli containerd.io

Start the Docker service and enable it to start on boot.

sudo systemctl start docker

sudo systemctl enable docker

Verify that Docker is installed correctly.

docker --version

If you see the Docker version, then you have successfully installed Docker on Fedora.

8.1.2 Podman

Install Podman and the Docker alias package.

dnf install podman podman-docker.noarch

Verify that Podman is installed correctly.

podman --version

If you see the Podman version, then you have successfully installed Podman on Fedora.

27
pgmoneta

The podman-docker.noarch package simplifies the use of Podman for users accustomed to
Docker.

8.2 Test suite

You can simply use CTest to test all PostgreSQL versions from 13 to 16. It will automatically run
testsuite.sh to test pgmoneta and pgmoneta_ext for each version. The script will automati-
cally create the Docker container, run it, and then use the check framework to test their functions
inside it. After that, it will automatically clean up everything for you.

Go to the directory /pgmoneta/test, and give permission to testsuite.sh using:

chmod +x testsuite.sh

After you follow the DEVELOPERS.md to install pgmoneta, go to the directory /pgmoneta/build
and run the test.

make test

CTest will output logs into /pgmoneta/build/Testing/Temporary/LastTest.log. If you

want to check the specific process, you can review that log file.

testsuite.sh accepts three variables. The first one is dir, which specifies the /test direc-
tory location, with a default value of ./. The second one is dockerfile, with a default value of
Dockerfile.rocky8. The third one is the PostgreSQL version, with a default value of 13.

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pgmoneta

9 WAL Reader

9.1 Overview

This document provides an overview of the wal_reader tool, with a focus on the parse_wal_file
function, which serves as the main entry point for parsing Write-Ahead Log (WAL) files. Currently, the
function only parses the given WAL file and prints the description of each record. In the future, it will
be integrated with other parts of the code.

9.2 pgmoneta-walinfo

pgmoneta-walinfo is a command line utility designed to read and display information about
PostgreSQL Write-Ahead Log (WAL) files. The tool provides output in either raw or JSON format,
making it easy to analyze WAL files for debugging, auditing, or general information purposes.

In addition to standard WAL files, pgmoneta-walinfo also supports encrypted (aes) and com-
pressed WAL files in the following formats: zstd, gz, lz4, and bz2.

9.2.0.1 Usage
pgmoneta-walinfo
Command line utility to read and display Write-Ahead Log (WAL) files

Usage:
pgmoneta-walinfo <file>

Options:
-c, --config CONFIG_FILE Set the path to the pgmoneta.conf file
-o, --output FILE Output file
-F, --format Output format (raw, json)
-L, --logfile FILE Set the log file
-q, --quiet No output only result
--color Use colors (on, off)
-v, --verbose Output result
-V, --version Display version information
-?, --help Display help

9.2.0.2 Raw Output Format In raw format, the default, the output is structured as follows:

Resource Manager | Start LSN | End LSN | rec len | tot len | xid |
description (data and backup)

• Resource Manager: The name of the resource manager handling the log record.
• Start LSN: The start Log Sequence Number (LSN).

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pgmoneta

• End LSN: The end Log Sequence Number (LSN).

• rec len: The length of the WAL record.
• tot len: The total length of the WAL record, including the header.
• xid: The transaction ID associated with the record.
• description (data and backup): A detailed description of the operation, along with any related
backup block information.

Each part of the output is color-coded:

• Red: Header information (resource manager, record length, transaction ID, etc.).
• Green: Description of the WAL record.
• Blue: Backup block references or additional data.

This format makes it easy to visually distinguish different parts of the WAL file for quick analysis.

9.2.0.3 Example To view WAL file details in JSON format:

pgmoneta-walinfo -F json /path/to/walfile

9.3 High-Level API Overview

The following section provides a high-level overview of how users can interact with the functions
and structures defined in the walfile.h file. These APIs allow you to read, write, and manage
Write-Ahead Log (WAL) files.

9.3.1 Struct walfile

The walfile struct represents the core structure used for interacting with WAL files in PostgreSQL. A
WAL file stores a log of changes to the database and is used for crash recovery, replication, and other
purposes. Each WAL file consists of pages (each 8192 bytes by default), containing records that capture
database changes.

9.3.1.1 Fields:

• magic_number: Identifies the PostgreSQL version that created the WAL file. You can find more
info on supported magic numbers here.
• long_phd: A pointer to the extended header (long header) found on the first page of the WAL file.
This header contains additional metadata.

30
pgmoneta

• page_headers: A deque of headers representing each page in the WAL file, excluding the first
page.
• records: A deque of decoded WAL records. Each record represents a change made to the database
and contains both metadata and the actual data to be applied during recovery or replication.

9.3.2 Function Overview

The walfile.h file provides three key functions for interacting with WAL files: pgmoneta_read_walfile
, pgmoneta_write_walfile, and pgmoneta_destroy_walfile. These functions allow
users to read from, write to, and destroy WAL file objects, respectively.

9.3.2.1 pgmoneta_read_walfile
int pgmoneta_read_walfile(int server, char* path, struct walfile** wf);

9.3.2.1.1 Description: This function reads a WAL file from a specified path and populates a
walfile structure with its contents, including the file’s headers and records.

9.3.2.1.2 Parameters:

• server: The index of the Postgres server in Pgmoneta configuration.

• path: The file path to the WAL file that needs to be read.
• wf: A pointer to a pointer to a walfile structure that will be populated with the WAL file data.

9.3.2.1.3 Return:

• Returns 0 on success or 1 on failure.

9.3.2.1.4 Usage Example:

struct walfile* wf = NULL;
int result = pgmoneta_read_walfile(0, "/path/to/walfile", &wf);
if (result == 0) {
// Successfully read WAL file
}

9.3.2.2 pgmoneta_write_walfile
int pgmoneta_write_walfile(struct walfile* wf, int server, char* path);

9.3.2.2.1 Description: This function writes the contents of a walfile structure back to disk, saving
it as a WAL file at the specified path.

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pgmoneta

9.3.2.2.2 Parameters:

• wf: The walfile structure containing the WAL data to be written.

• server: The index or ID of the server where the WAL file should be saved.
• path: The file path where the WAL file should be written.

9.3.2.2.3 Return:

• Returns 0 on success or 1 on failure.

9.3.2.2.4 Usage Example:

int result = pgmoneta_write_walfile(wf, 0, "/path/to/output_walfile");
if (result == 0) {
// Successfully wrote WAL file
}

9.3.2.3 pgmoneta_destroy_walfile
void pgmoneta_destroy_walfile(struct walfile* wf);

9.3.2.3.1 Description: This function frees the memory allocated for a walfile structure, including
its headers and records.

9.3.2.3.2 Parameters:

• wf: The walfile structure to be destroyed.

9.3.2.3.3 Usage Example:

struct walfile* wf = NULL;
int result = pgmoneta_read_walfile(0, "/path/to/walfile", &wf);
if (result == 0) {
// Successfully read WAL file
}
pgmoneta_destroy_walfile(wf);

9.4 Internal API Overview

9.4.1 parse_wal_file

This function is responsible for reading and parsing a PostgreSQL Write-Ahead Log (WAL) file.

32
pgmoneta

9.4.1.1 Parameters

• path: The file path to the WAL file that needs to be parsed.
• server_info: A pointer to a server structure containing information about the server.

9.4.1.2 Description The parse_wal_file function opens the WAL file specified by the path
parameter in binary mode and reads the WAL records. It processes these records, handling various cases
such as records that cross page boundaries, while ensuring correct memory management throughout
the process.

9.4.2 Usage Example

parse_wal_file("/path/to/wal/file", &my_server);

9.4.3 WAL File Structure

The image illustrates the structure of a WAL (Write-Ahead Logging) file in PostgreSQL, focusing on how
XLOG records are organized within WAL segments.

Source: https://www.interdb.jp/pg/pgsql09/03.html

Figure 1: WAL File Structure

A WAL segment, by default, is a 16 MB file, divided into pages of 8192 bytes (8 KB) each. The first page
contains a header defined by the XLogLongPageHeaderData structure, while all subsequent pages

33
pgmoneta

have headers described by the XLogPageHeaderData structure. XLOG records are written sequentially
in each page, starting at the beginning and moving downward.

The figure highlights how the WAL ensures data consistency by sequentially writing XLOG records in
pages, structured within larger 16 MB WAL segments.

9.5 Resource Managers

In the context of the WAL reader, resource managers (rm) are responsible for handling different types
of records found within a WAL file. Each record in the WAL file is associated with a specific resource
manager, which determines how that record is processed.

9.5.1 Resource Manager Definitions

Each resource manager is defined in the rm_[name].h header file and implemented in the corre-
sponding rm_[name].c source file.

In the rmgr.h header file, the resource managers are declared as an enum, with each resource
manager having a unique identifier.

9.5.2 Resource Manager Functions

Each resource manager implements the rm_desc function, which provides a description of the record
type associated with that resource manager. In the future, they will be extended to implement the
rm_redo function to apply the changes to another server.

9.5.3 Supporting Various WAL Structures in PostgreSQL Versions 13 to 17

The WAL structure has evolved across PostgreSQL versions 13 to 17, requiring different handling for
each version. To accommodate these differences, we have implemented a wrapper-based approach,
such as the factory pattern, to handle varying WAL structures.

Below are the commit hashes for the officially supported magic values in each PostgreSQL version:

1. PostgreSQL 13 - 0xD106: https://github.com/postgres/postgres/commit/c6b92041d38512a4176ed76ad06f713d2e

2. PostgreSQL 14 - 0xD10D: https://github.com/postgres/postgres/commit/08aa89b326261b669648df97d4f2a6edba

34
pgmoneta

3. PostgreSQL 15 - 0xD110: https://github.com/postgres/postgres/commit/8b1dccd37c71ed2ff016294d8f9053a32b0

4. PostgreSQL 16 - 0xD113: https://github.com/postgres/postgres/commit/6af1793954e8c5e753af83c3edb37ed3267

5. PostgreSQL 17 - 0xD116: https://github.com/postgres/postgres/commit/402b586d0a9caae9412d25fcf1b91dae453

xl_end_of_recovery is an example of how we handle different versions of structures with a

wrapper struct and a factory pattern.

struct xl_end_of_recovery_v16 {
timestamp_tz end_time;
timeline_id this_timeline_id;
timeline_id prev_timeline_id;
};

struct xl_end_of_recovery_v17 {
timestamp_tz end_time;
timeline_id this_timeline_id;
timeline_id prev_timeline_id;
int wal_level;
};

struct xl_end_of_recovery {
int pg_version;
union {
struct xl_end_of_recovery_v16 v16;
struct xl_end_of_recovery_v17 v17;
} data;
void (*parse)(struct xl_end_of_recovery* wrapper, const void* rec);
char* (*format)(struct xl_end_of_recovery* wrapper, char* buf);
};

xl_end_of_recovery* create_xl_end_of_recovery(int pg_version) {

xl_end_of_recovery* wrapper = malloc(sizeof(xl_end_of_recovery));
wrapper->pg_version = pg_version;

if (pg_version >= 17) {

wrapper->parse = parse_v17;
wrapper->format = format_v17;
} else {
wrapper->parse = parse_v16;
wrapper->format = format_v16;
}

return wrapper;
}

void parse_v16(xl_end_of_recovery* wrapper, const void* rec) {

memcpy(&wrapper->data.v16, rec, sizeof(struct xl_end_of_recovery_v16))

35
pgmoneta

;
}

void parse_v17(xl_end_of_recovery* wrapper, const void* rec) {

memcpy(&wrapper->data.v17, rec, sizeof(struct xl_end_of_recovery_v17))
;
}

char* format_v16(xl_end_of_recovery* wrapper, char* buf) {

struct xl_end_of_recovery_v16* xlrec = &wrapper->data.v16;
return pgmoneta_format_and_append(buf, "tli %u; prev tli %u; time %s",
xlrec->this_timeline_id, xlrec->
prev_timeline_id,
pgmoneta_wal_timestamptz_to_str(
xlrec->end_time));
}

char* format_v17(xl_end_of_recovery* wrapper, char* buf) {

struct xl_end_of_recovery_v17* xlrec = &wrapper->data.v17;
return pgmoneta_format_and_append(buf, "tli %u; prev tli %u; time %s;
wal_level %d",
xlrec->this_timeline_id, xlrec->
prev_timeline_id,
pgmoneta_wal_timestamptz_to_str(
xlrec->end_time),
xlrec->wal_level);
}

9.6 WAL Change List

This section lists the changes in the WAL format between different versions of PostgreSQL.

9.6.1 xl_clog_truncate

17

struct xl_clog_truncate
{
int64 pageno; /**< The page number of the clog to truncate
*/
transaction_id oldestXact; /**< The oldest transaction ID to retain */
oid oldestXactDb; /**< The database ID of the oldest transaction
*/
};

16

36
pgmoneta

struct xl_clog_truncate
{
int64 pageno; /**< The page number of the clog to truncate
*/
transaction_id oldestXact; /**< The oldest transaction ID to retain */
oid oldestXactDb; /**< The database ID of the oldest transaction
*/
};

9.6.2 xl_commit_ts_truncate

17:

typedef struct xl_commit_ts_truncate

{
int64 pageno;
TransactionId oldestXid;
} xl_commit_ts_truncate;

16:

typedef struct xl_commit_ts_truncate

{
int pageno;
TransactionId oldestXid;
} xl_commit_ts_truncate;

9.6.3 xl_heap_prune

17:

typedef struct xl_heap_prune

{
uint8 reason;
uint8 flags;

/*
* If XLHP_HAS_CONFLICT_HORIZON is set, the conflict horizon XID
follows,
* unaligned
*/
} xl_heap_prune;
#define SizeOfHeapPrune (offsetof(xl_heap_prune, flags) + sizeof(uint8))

16:

37
pgmoneta

typedef struct xl_heap_prune

{
TransactionId snapshotConflictHorizon;
uint16 nredirected;
uint16 ndead;
bool isCatalogRel; /* to handle recovery conflict during
logical
* decoding on standby */
/* OFFSET NUMBERS are in the block reference 0 */
} xl_heap_prune;
#define SizeOfHeapPrune (offsetof(xl_heap_prune, isCatalogRel) + sizeof(
bool))

9.6.4 xlhp_freeze_plan

Removed xl_heap_freeze_page

17:

typedef struct xlhp_freeze_plan

{
TransactionId xmax;
uint16 t_infomask2;
uint16 t_infomask;
uint8 frzflags;

/* Length of individual page offset numbers array for this plan */

uint16 ntuples;
} xlhp_freeze_plan;

9.6.5 spgxlogState

(Doesn’t need to be changed)

17:

typedef struct spgxlogState

{
TransactionId redirectXid;
bool isBuild;
} spgxlogState;

16:

typedef struct spgxlogState

{
TransactionId myXid;

38
pgmoneta

bool isBuild;
} spgxlogState;

9.6.6 xl_end_of_recovery

typedef struct xl_end_of_recovery

{
TimestampTz end_time;
TimeLineID ThisTimeLineID; /* new TLI */
TimeLineID PrevTimeLineID; /* previous TLI we forked off from */
int wal_level;
} xl_end_of_recovery;

16:

typedef struct xl_end_of_recovery

{
TimestampTz end_time;
TimeLineID ThisTimeLineID; /* new TLI */
TimeLineID PrevTimeLineID; /* previous TLI we forked off from */
} xl_end_of_recovery;

16 → 15

9.6.7 gingxlogSplit

16: same for gin_xlog_update_meta

typedef struct ginxlogSplit

{
RelFileLocator locator;
BlockNumber rrlink; /* right link, or root’s blocknumber if
root
* split */
BlockNumber leftChildBlkno; /* valid on a non-leaf split */
BlockNumber rightChildBlkno;
uint16 flags; /* see below */
} ginxlogSplit;

15:

typedef struct ginxlogSplit

{

39
pgmoneta

RelFileNode node;
BlockNumber rrlink; /* right link, or root’s blocknumber if
root
* split */
BlockNumber leftChildBlkno; /* valid on a non-leaf split */
BlockNumber rightChildBlkno;
uint16 flags; /* see below */
} ginxlogSplit;

9.6.8 gistxlogDelete

16:

typedef struct gistxlogDelete

{
TransactionId snapshotConflictHorizon;
uint16 ntodelete; /* number of deleted offsets */
bool isCatalogRel; /* to handle recovery conflict during
logical
* decoding on standby */

/* TODELETE OFFSET NUMBERS */

OffsetNumber offsets[FLEXIBLE_ARRAY_MEMBER];
} gistxlogDelete;
#define SizeOfGistxlogDelete offsetof(gistxlogDelete, offsets)

15:

typedef struct gistxlogDelete

{
TransactionId latestRemovedXid;
uint16 ntodelete; /* number of deleted offsets */

/*
* In payload of blk 0 : todelete OffsetNumbers
*/
} gistxlogDelete;
#define SizeOfGistxlogDelete (offsetof(gistxlogDelete, ntodelete) +
sizeof(uint16))

9.6.9 gistxlogPageReuse

16:

typedef struct gistxlogPageReuse

{
RelFileLocator locator;

40
pgmoneta

BlockNumber block;
FullTransactionId snapshotConflictHorizon;
bool isCatalogRel; /* to handle recovery conflict during
logical
* decoding on standby */
} gistxlogPageReuse;
#define SizeOfGistxlogPageReuse (offsetof(gistxlogPageReuse, isCatalogRel)
+ sizeof(bool))

15:

typedef struct gistxlogPageReuse

{
RelFileNode node;
BlockNumber block;
FullTransactionId latestRemovedFullXid;
} gistxlogPageReuse;

#define SizeOfGistxlogPageReuse (offsetof(gistxlogPageReuse,

latestRemovedFullXid) + sizeof(FullTransactionId))

9.6.10 xl_hash_vacuum_one_page

16:

typedef struct xl_hash_vacuum_one_page

{
TransactionId snapshotConflictHorizon;
uint16 ntuples;
bool isCatalogRel; /* to handle recovery conflict during
logical
* decoding on standby */

/* TARGET OFFSET NUMBERS */

OffsetNumber offsets[FLEXIBLE_ARRAY_MEMBER];
} xl_hash_vacuum_one_page;
#define SizeOfHashVacuumOnePage offsetof(xl_hash_vacuum_one_page, offsets)

15:

typedef struct xl_hash_vacuum_one_page

{
TransactionId latestRemovedXid;
int ntuples;

/* TARGET OFFSET NUMBERS FOLLOW AT THE END */

} xl_hash_vacuum_one_page;
#define SizeOfHashVacuumOnePage \
(offsetof(xl_hash_vacuum_one_page, ntuples) + sizeof(int))

41
pgmoneta

9.6.11 xl_heap_prune

16:

typedef struct xl_heap_prune

{
TransactionId snapshotConflictHorizon;
uint16 nredirected;
uint16 ndead;
bool isCatalogRel; /* to handle recovery conflict during
logical
* decoding on standby */
/* OFFSET NUMBERS are in the block reference 0 */
} xl_heap_prune;
#define SizeOfHeapPrune (offsetof(xl_heap_prune, isCatalogRel) + sizeof(
bool))

15:

typedef struct xl_heap_prune

{
TransactionId latestRemovedXid;
uint16 nredirected;
uint16 ndead;
/* OFFSET NUMBERS are in the block reference 0 */
} xl_heap_prune;
#define SizeOfHeapPrune (offsetof(xl_heap_prune, ndead) + sizeof(uint16))

9.6.12 xl_heap_freeze_plan

16:

typedef struct xl_heap_freeze_plan

{
TransactionId xmax;
uint16 t_infomask2;
uint16 t_infomask;
uint8 frzflags;

/* Length of individual page offset numbers array for this plan */

uint16 ntuples;
} xl_heap_freeze_plan;

15:

typedef struct xl_heap_freeze_tuple

{
TransactionId xmax;
OffsetNumber offset;

42
pgmoneta

uint16 t_infomask2;
uint16 t_infomask;
uint8 frzflags;
} xl_heap_freeze_tuple;

9.6.13 xl_heap_freeze_page

16:

typedef struct xl_heap_freeze_page

{
TransactionId snapshotConflictHorizon;
uint16 nplans;
bool isCatalogRel; /* to handle recovery conflict during
logical
* decoding on standby */

/*
* In payload of blk 0 : FREEZE PLANS and OFFSET NUMBER ARRAY
*/
} xl_heap_freeze_page;

15:

typedef struct xl_heap_freeze_page

{
TransactionId cutoff_xid;
uint16 ntuples;
} xl_heap_freeze_page;

9.6.14 xl_btree_reuse_page

16:

typedef struct xl_btree_reuse_page

{
RelFileLocator locator;
BlockNumber block;
FullTransactionId snapshotConflictHorizon;
bool isCatalogRel; /* to handle recovery conflict during
logical
* decoding on standby */
} xl_btree_reuse_page;

15:

typedef struct xl_btree_reuse_page

43
pgmoneta

{
RelFileNode node;
BlockNumber block;
FullTransactionId latestRemovedFullXid;
} xl_btree_reuse_page;

9.6.15 xl_btree_delete

16:

typedef struct xl_btree_delete

{
TransactionId snapshotConflictHorizon;
uint16 ndeleted;
uint16 nupdated;
bool isCatalogRel; /* to handle recovery conflict during
logical
* decoding on standby */

/*----
* In payload of blk 0 :
* - DELETED TARGET OFFSET NUMBERS
* - UPDATED TARGET OFFSET NUMBERS
* - UPDATED TUPLES METADATA (xl_btree_update) ARRAY
*----
*/
} xl_btree_delete;

15:

typedef struct xl_btree_delete

{
TransactionId latestRemovedXid;
uint16 ndeleted;
uint16 nupdated;

/* DELETED TARGET OFFSET NUMBERS FOLLOW */

/* UPDATED TARGET OFFSET NUMBERS FOLLOW */
/* UPDATED TUPLES METADATA (xl_btree_update) ARRAY FOLLOWS */
} xl_btree_delete;

9.6.16 spgxlogVacuumRedirect

16:

typedef struct spgxlogVacuumRedirect

{

44
pgmoneta

uint16 nToPlaceholder; /* number of redirects to make

placeholders */
OffsetNumber firstPlaceholder; /* first placeholder tuple to remove
*/
TransactionId snapshotConflictHorizon; /* newest XID of removed
redirects */
bool isCatalogRel; /* to handle recovery conflict during
logical
* decoding on standby */

/* offsets of redirect tuples to make placeholders follow */

OffsetNumber offsets[FLEXIBLE_ARRAY_MEMBER];
} spgxlogVacuumRedirect;

15:

typedef struct spgxlogVacuumRedirect

{
uint16 nToPlaceholder; /* number of redirects to make
placeholders */
OffsetNumber firstPlaceholder; /* first placeholder tuple to remove
*/
TransactionId newestRedirectXid; /* newest XID of removed redirects
*/

/* offsets of redirect tuples to make placeholders follow */

OffsetNumber offsets[FLEXIBLE_ARRAY_MEMBER];
} spgxlogVacuumRedirect;

15 → 14

9.6.17 xl_xact_prepare

15:

ctypedef struct xl_xact_prepare

{
uint32 magic; /* format identifier */
uint32 total_len; /* actual file length */
TransactionId xid; /* original transaction XID */
Oid database; /* OID of database it was in */
TimestampTz prepared_at; /* time of preparation */
Oid owner; /* user running the transaction */
int32 nsubxacts; /* number of following subxact XIDs */
int32 ncommitrels; /* number of delete-on-commit rels */
int32 nabortrels; /* number of delete-on-abort rels */

45
pgmoneta

int32 ncommitstats; /* number of stats to drop on commit */

int32 nabortstats; /* number of stats to drop on abort */
int32 ninvalmsgs; /* number of cache invalidation messages
*/
bool initfileinval; /* does relcache init file need
invalidation? */
uint16 gidlen; /* length of the GID - GID follows the
header */
XLogRecPtr origin_lsn; /* lsn of this record at origin node */
TimestampTz origin_timestamp; /* time of prepare at origin node */
} xl_xact_prepare;

14:

typedef struct xl_xact_prepare

{
uint32 magic; /* format identifier */
uint32 total_len; /* actual file length */
TransactionId xid; /* original transaction XID */
Oid database; /* OID of database it was in */
TimestampTz prepared_at; /* time of preparation */
Oid owner; /* user running the transaction */
int32 nsubxacts; /* number of following subxact XIDs */
int32 ncommitrels; /* number of delete-on-commit rels */
int32 nabortrels; /* number of delete-on-abort rels */
int32 ninvalmsgs; /* number of cache invalidation messages
*/
bool initfileinval; /* does relcache init file need
invalidation? */
uint16 gidlen; /* length of the GID - GID follows the
header */
XLogRecPtr origin_lsn; /* lsn of this record at origin node */
TimestampTz origin_timestamp; /* time of prepare at origin node */
} xl_xact_prepare;

9.6.18 xl_xact_parsed_commit

15:

typedef struct xl_xact_parsed_commit

{
TimestampTz xact_time;
uint32 xinfo;

Oid dbId; /* MyDatabaseId */

Oid tsId; /* MyDatabaseTableSpace */

int nsubxacts;
TransactionId *subxacts;

46
pgmoneta

int nrels;
RelFileNode *xnodes;

int nstats;
xl_xact_stats_item *stats;

int nmsgs;
SharedInvalidationMessage *msgs;

TransactionId twophase_xid; /* only for 2PC */

char twophase_gid[GIDSIZE]; /* only for 2PC */
int nabortrels; /* only for 2PC */
RelFileNode *abortnodes; /* only for 2PC */
int nabortstats; /* only for 2PC */
xl_xact_stats_item *abortstats; /* only for 2PC */

XLogRecPtr origin_lsn;
TimestampTz origin_timestamp;
} xl_xact_parsed_commit;

14:

typedef struct xl_xact_parsed_commit

{
TimestampTz xact_time;
uint32 xinfo;

Oid dbId; /* MyDatabaseId */

Oid tsId; /* MyDatabaseTableSpace */

int nsubxacts;
TransactionId *subxacts;

int nrels;
RelFileNode *xnodes;

int nmsgs;
SharedInvalidationMessage *msgs;

TransactionId twophase_xid; /* only for 2PC */

char twophase_gid[GIDSIZE]; /* only for 2PC */
int nabortrels; /* only for 2PC */
RelFileNode *abortnodes; /* only for 2PC */

XLogRecPtr origin_lsn;
TimestampTz origin_timestamp;
} xl_xact_parsed_commit;

47
pgmoneta

9.6.19 xl_xact_parsed_abort

15:

typedef struct xl_xact_parsed_abort

{
TimestampTz xact_time;
uint32 xinfo;

Oid dbId; /* MyDatabaseId */

Oid tsId; /* MyDatabaseTableSpace */

int nsubxacts;
TransactionId *subxacts;

int nrels;
RelFileNode *xnodes;

int nstats;
xl_xact_stats_item *stats;

TransactionId twophase_xid; /* only for 2PC */

char twophase_gid[GIDSIZE]; /* only for 2PC */

XLogRecPtr origin_lsn;
TimestampTz origin_timestamp;
} xl_xact_parsed_abort;

14:

typedef struct xl_xact_parsed_abort

{
TimestampTz xact_time;
uint32 xinfo;

Oid dbId; /* MyDatabaseId */

Oid tsId; /* MyDatabaseTableSpace */

int nsubxacts;
TransactionId *subxacts;

int nrels;
RelFileNode *xnodes;

TransactionId twophase_xid; /* only for 2PC */

char twophase_gid[GIDSIZE]; /* only for 2PC */

XLogRecPtr origin_lsn;
TimestampTz origin_timestamp;
} xl_xact_parsed_abort;

48
pgmoneta

9.6.20 xlogrecord.h flags

15:

#define BKPIMAGE_APPLY 0x02 /* page image should be restored

* during replay */
/* compression methods supported */
#define BKPIMAGE_COMPRESS_PGLZ 0x04
#define BKPIMAGE_COMPRESS_LZ4 0x08
#define BKPIMAGE_COMPRESS_ZSTD 0x10

#define BKPIMAGE_COMPRESSED(info) \
((info & (BKPIMAGE_COMPRESS_PGLZ | BKPIMAGE_COMPRESS_LZ4 | \
BKPIMAGE_COMPRESS_ZSTD)) != 0)

14:

#define BKPIMAGE_IS_COMPRESSED 0x02 /* page image is compressed */

#define BKPIMAGE_APPLY 0x04 /* page image should be restored
during
* replay */

14 → 13

9.6.21 xl_heap_prune

14:

typedef struct xl_heap_prune

{
TransactionId latestRemovedXid;
uint16 nredirected;
uint16 ndead;
/* OFFSET NUMBERS are in the block reference 0 */
} xl_heap_prune;

13:

typedef struct xl_heap_clean

{
TransactionId latestRemovedXid;
uint16 nredirected;
uint16 ndead;
/* OFFSET NUMBERS are in the block reference 0 */
} xl_heap_clean;

49
pgmoneta

9.6.22 xl_heap_vacuum

14:

typedef struct xl_heap_vacuum

{
uint16 nunused;
/* OFFSET NUMBERS are in the block reference 0 */
} xl_heap_vacuum;

13:

typedef struct xl_heap_cleanup_info

{
RelFileNode node;
TransactionId latestRemovedXid;
} xl_heap_cleanup_info;

9.6.23 xl_btree_metadata

14:

typedef struct xl_btree_metadata

{
uint32 version;
BlockNumber root;
uint32 level;
BlockNumber fastroot;
uint32 fastlevel;
uint32 last_cleanup_num_delpages;
bool allequalimage;
} xl_btree_metadata;

13:

typedef struct xl_btree_metadata

{
uint32 version;
BlockNumber root;
uint32 level;
BlockNumber fastroot;
uint32 fastlevel;
TransactionId oldest_btpo_xact;
float8 last_cleanup_num_heap_tuples;
bool allequalimage;
} xl_btree_metadata;

50
pgmoneta

9.6.24 xl_btree_reuse_page

14:

typedef struct xl_btree_reuse_page

{
RelFileNode node;
BlockNumber block;
FullTransactionId latestRemovedFullXid;
} xl_btree_reuse_page;

13:

typedef struct xl_btree_reuse_page

{
RelFileNode node;
BlockNumber block;
TransactionId latestRemovedXid;
} xl_btree_reuse_page;

9.6.25 xl_btree_delete

14:

typedef struct xl_btree_delete

{
TransactionId latestRemovedXid;
uint16 ndeleted;
uint16 nupdated;

/* DELETED TARGET OFFSET NUMBERS FOLLOW */

/* UPDATED TARGET OFFSET NUMBERS FOLLOW */
/* UPDATED TUPLES METADATA (xl_btree_update) ARRAY FOLLOWS */
} xl_btree_delete;

13:

typedef struct xl_btree_delete

{
TransactionId latestRemovedXid;
uint32 ndeleted;

/* DELETED TARGET OFFSET NUMBERS FOLLOW */

} xl_btree_delete;

51
pgmoneta

9.6.26 xl_btree_unlink_page

14:

typedef struct xl_btree_unlink_page

{
BlockNumber leftsib; /* target block’s left sibling, if any */
BlockNumber rightsib; /* target block’s right sibling */
uint32 level; /* target block’s level */
FullTransactionId safexid; /* target block’s BTPageSetDeleted() XID
*/

/*
* Information needed to recreate a half-dead leaf page with correct
* topparent link. The fields are only used when deletion operation’s
* target page is an internal page. REDO routine creates half-dead
page
* from scratch to keep things simple (this is the same convenient
* approach used for the target page itself).
*/
BlockNumber leafleftsib;
BlockNumber leafrightsib;
BlockNumber leaftopparent; /* next child down in the subtree */

/* xl_btree_metadata FOLLOWS IF XLOG_BTREE_UNLINK_PAGE_META */

} xl_btree_unlink_page;

13:

typedef struct xl_btree_unlink_page

{
BlockNumber leftsib; /* target block’s left sibling, if any */
BlockNumber rightsib; /* target block’s right sibling */

/*
* Information needed to recreate the leaf page, when target is an
* internal page.
*/
BlockNumber leafleftsib;
BlockNumber leafrightsib;
BlockNumber topparent; /* next child down in the branch */

TransactionId btpo_xact; /* value of btpo.xact for use in recovery

*/
/* xl_btree_metadata FOLLOWS IF XLOG_BTREE_UNLINK_PAGE_META */
} xl_btree_unlink_page;

52
pgmoneta

9.7 Additional Information

For more details on the internal workings and additional helper functions used in parse_wal_file,
refer to the source code in wal_reader.c.

53
pgmoneta

10 Troubleshooting

10.1 Could not get version for server

If you get this FATAL during startup check your PostgreSQL logins

psql postgres

and

psql -U repl postgres

And, check the PostgreSQL logs for any error.

Setting log_level to DEBUG5 in pgmoneta.conf could provide more information about the
error.

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pgmoneta

11 Acknowledgement

11.1 Authors

pgmoneta was created by the following authors:

Jesper Pedersen <jesper.pedersen@comcast.net>

David Fetter <david@fetter.org>
Will Leinweber <will@bitfission.com>
Luca Ferrari <fluca1978@gmail.com>
Nikita Bugrovsky <nbugrovs@redhat.com>
Mariam Fahmy <mariamfahmy66@gmail.com>
Jichen Xu <kyokitisin@gmail.com>
Saurav Pal <resyfer.dev@gmail.com>
Bokket <bokkett@gmail.com>
Haoran Zhang <andrewzhr9911@gmail.com>
Hazem Alrawi <hazemalrawi7@gmail.com>
Shahryar Soltanpour <shahryar.soltanpour@gmail.com>
Shikhar Soni <shikharish05@gmail.com>
Nguyen Cong Nhat Le <lenguyencongnhat2001@gmail.com>
Chao Gu <chadraven369@gmail.com>
Luchen Zhao <lucian.zlc@gmail.com>
Joan Jeremiah J <joanjeremiah04@gmail.com>
Iury Santos <iuryroberto@gmail.com>
Palak Chaturvedi <palakchaturvedi2843@gmail.com>
Jakub Jirutka <jakub@jirutka.cz>
Mario Rodas

11.2 Committers

Jesper Pedersen <jesper.pedersen@comcast.net>

Haoran Zhang <andrewzhr9911@gmail.com>

11.3 Contributing

Contributions to pgmoneta are managed on GitHub

• Ask a question
• Raise an issue
• Feature request
• Code submission

Contributions are most welcome!

Please, consult our Code of Conduct policies for interacting in our community.

55
pgmoneta

Consider giving the project a star on GitHub if you find it useful. And, feel free to follow the project on
Twitter as well.

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pgmoneta

12 License

Copyright (C) 2025 The pgmoneta community

Redistribution and use in source and binary forms, with or without

modification, are permitted provided that the following conditions
are met:

1. Redistributions of source code must retain the above copyright

notice, this list of conditions and the following disclaimer.

2. Redistributions in binary form must reproduce the above

copyright notice, this list of conditions and the following
disclaimer in the documentation and/or other materials provided
with the distribution.

3. Neither the name of the copyright holder nor the names of

its contributors may be used to endorse or promote products
derived from this software without specific prior written
permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS

"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
OF SUCH DAMAGE.

BSD-3-Clause

12.1 libart

Our adaptive radix tree (ART) implementation is based on The Adaptive Radix Tree: ARTful Indexing for
Main-Memory Databases and libart which has a 3-BSD license as

Copyright (c) 2012, Armon Dadgar

All rights reserved.

Redistribution and use in source and binary forms, with or without

modification, are permitted provided that the following conditions
are met:

57
pgmoneta

* Redistributions of source code must retain the above copyright

notice, this list of conditions and the following disclaimer.

* Redistributions in binary form must reproduce the above copyright

notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.

* Neither the name of the organization nor the

names of its contributors may be used to endorse or promote products
derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS

"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL ARMON DADGAR
BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

58