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Add CacheBehavior::AUTOMATIC to DBInstanceCache that automatically does the right thing™ #19841

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Merged
Mytherin merged 1 commit into from
Nov 19, 2025
+45 −2
Merged

Add CacheBehavior::AUTOMATIC to DBInstanceCache that automatically does the right thing™ #19841

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5 changes: 5 additions & 0 deletions src/include/duckdb/main/db_instance_cache.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,8 @@ struct DatabaseCacheEntry {
mutex update_database_mutex;
};

enum class CacheBehavior { AUTOMATIC, ALWAYS_CACHE, NEVER_CACHE };

class DBInstanceCache {
public:
DBInstanceCache();
Expand All @@ -41,6 +43,9 @@ class DBInstanceCache {
//! Either returns an existing entry, or creates and caches a new DB Instance
shared_ptr<DuckDB> GetOrCreateInstance(const string &database, DBConfig &config_dict, bool cache_instance,
const std::function<void(DuckDB &)> &on_create = nullptr);
shared_ptr<DuckDB> GetOrCreateInstance(const string &database, DBConfig &config_dict,
CacheBehavior cache_behavior = CacheBehavior::AUTOMATIC,
const std::function<void(DuckDB &)> &on_create = nullptr);

private:
shared_ptr<DatabaseFilePathManager> path_manager;
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2 changes: 1 addition & 1 deletion src/main/capi/duckdb-c.cpp
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Expand Up @@ -41,7 +41,7 @@ duckdb_state duckdb_open_internal(DBInstanceCacheWrapper *cache, const char *pat
if (path) {
path_str = path;
}
wrapper->database = cache->instance_cache->GetOrCreateInstance(path_str, *db_config, true);
wrapper->database = cache->instance_cache->GetOrCreateInstance(path_str, *db_config);
} else {
wrapper->database = duckdb::make_shared_ptr<DuckDB>(path, db_config);
}
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16 changes: 15 additions & 1 deletion src/main/db_instance_cache.cpp
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Expand Up @@ -137,9 +137,23 @@ shared_ptr<DuckDB> DBInstanceCache::CreateInstance(const string &database, DBCon
shared_ptr<DuckDB> DBInstanceCache::GetOrCreateInstance(const string &database, DBConfig &config_dict,
bool cache_instance,
const std::function<void(DuckDB &)> &on_create) {
auto cache_behavior = cache_instance ? CacheBehavior::ALWAYS_CACHE : CacheBehavior::NEVER_CACHE;
return GetOrCreateInstance(database, config_dict, cache_behavior, on_create);
}

shared_ptr<DuckDB> DBInstanceCache::GetOrCreateInstance(const string &database, DBConfig &config_dict,
CacheBehavior cache_behavior,
const std::function<void(DuckDB &)> &on_create) {
unique_lock<mutex> lock(cache_lock, std::defer_lock);
bool cache_instance = cache_behavior == CacheBehavior::ALWAYS_CACHE;
if (cache_behavior == CacheBehavior::AUTOMATIC) {
// cache all unnamed in-memory connections
cache_instance = true;
if (database == IN_MEMORY_PATH || database.empty()) {
cache_instance = false;
}
}
if (cache_instance) {

// While we do not own the lock, we cannot definitively say that the database instance does not exist.
while (!lock.owns_lock()) {
// The problem is, that we have to unlock the mutex in GetInstanceInternal, so we can non-blockingly wait
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24 changes: 24 additions & 0 deletions test/api/test_instance_cache.cpp
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Expand Up @@ -205,3 +205,27 @@ TEST_CASE("Test attaching the same database path from different databases in rea
REQUIRE_FAIL(con1.Query(read_only_attach));
}
}

TEST_CASE("Test automatic DB instance caching", "[api][.]") {
DBInstanceCache instance_cache;
DBConfig config;

SECTION("Unnamed in-memory connections are not shared") {
auto db1 = instance_cache.GetOrCreateInstance(":memory:", config);
auto db2 = instance_cache.GetOrCreateInstance(":memory:", config);

Connection con(*db1);
Connection con2(*db2);
REQUIRE_NO_FAIL(con.Query("CREATE TABLE t(i INT)"));
REQUIRE_NO_FAIL(con2.Query("CREATE TABLE t(i INT)"));
}
SECTION("Named in-memory connections are shared") {
auto db1 = instance_cache.GetOrCreateInstance(":memory:abc", config);
auto db2 = instance_cache.GetOrCreateInstance(":memory:abc", config);

Connection con(*db1);
Connection con2(*db2);
REQUIRE_NO_FAIL(con.Query("CREATE TABLE t(i INT)"));
REQUIRE_NO_FAIL(con2.Query("SELECT * FROM t"));
}
}
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