Reduce disk I/O of time-based compaction#6169
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When the partition transformer (used by compaction) creates output partitions, it was copying the source partition's full min/max import time range onto every output partition synopsis. That makes the compacted partition's time range overlap the original input range, so time-based compaction rules consider it eligible for compaction again on the next run. Aggregate min/max import time from the slices that actually end up in each output partition instead, so the resulting partition's range reflects its actual contents.
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🔍 Problem
When a time-based compaction rule deletes part of a partition's data, the
output partition's synopsis should reflect the time range of the slices that
survived. Instead, the old code copied the input partition's full
min_import_time/max_import_timeonto the output synopsis.So an input partition spanning a wide time range that's been trimmed by
compaction kept advertising the original wide range. Time-based compaction
rules use that range to pick eligible partitions, so the same partition got
selected and rewritten again on every run, even though there was nothing
left to do.
🛠️ Solution
min/maximport time from the slices that actually end up ineach output partition with
std::min/std::max.partition_synopsissentinels (min_import_time = time::max(),max_import_time = time::min()) make the first slice seed the rangecorrectly.
💬 Review
- Side fix discovered while investigating TNZ-527; should not close that
- No new test — the existing transformer/compaction tests don't assert on
🎫 References TNZ-527ticket.
per-partition import-time ranges. Happy to add one if you want.