improve ps gc speed by dumping snapshot from memory directly #7668
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Co-authored-by: JaySon <tshent@qq.com>
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[APPROVALNOTIFIER] This PR is APPROVED This pull-request has been approved by: flowbehappy, JaySon-Huang The full list of commands accepted by this bot can be found here. The pull request process is described here
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This was referenced Jul 13, 2023
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What problem does this PR solve?
Issue Number: ref #6827
Problem Summary: Previously, when dumping snapshot for
PageDirectory, we load all target wal files and create a temp PageDirectory for dumping. And after dumping the snapshot, we can reclaim all the target wal files.But under heavy write scenario, the dump snapshot speed is a little slow. This will make the number of wal files keep increasing and make the process of dumping snapshot cost more and more memory.
What is changed and how it works?
Change the type of
being_ref_countfromInt64toMultiVersionRefCount *;being_ref_countis nullptr, it means1;PageVersion -> RefCountinsideMultiVersionRefCount;getLatestRefCountandappendRefCount;decrLatestRefCountInSnap. And it will also reclaim older version of ref count;When dumping snapshot, ref count increasing caused by new ref page will just be appended to
MultiVersionRefCount, so it won't affect the ref count value that the snapshot can see.GC process can still change ref count value for a snapshot, but it doesn't matter because gc won't run concurrently with dumping snapshot.
Check List
Tests
Side effects
Documentation
Release note