[HBASE-26144] The HStore.snapshot method is never called in main code

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 2.5.0, 3.0.0-alpha-2
• Component/s: regionserver
• Hadoop Flags: Reviewed
• Assignee: Duo Zhang
• Reporter: Duo Zhang
• Created: 27/Jul/21 11:41
• Updated: 21/Nov/21 12:35
• Resolved: 31/Jul/21 07:29

Description

In the comment of HStore.flushCache, we say that HStore.snapshot method must be called first. But actually, we will call memstore.snapshot directly from StoreFlusherImpl.prepare, without holding the write lock. The reason we do not need to hold the write lock is that, we hold HRegion.updatesLock in the upper layer, so it is OK.

See HBASE-10087 for more discussion about this.

So in general, I think we could remove the snapshot method in HStore. And I do not think we need to hold the write lock when calling clearSnapshot then. As in the HRegion layer, we need to guarantee that there is only one ongoing flush of the region, so before we finish the region, it is already safe to operate on the snapshot of the memstore, especially that the clearSnapshot method itself is thread safe.

Issue Links

• causes: HBASE-26465 MemStoreLAB may be released early when its SegmentScanner is scanning
• is related to: HBASE-26067 Change the way on how we track store file list
• links to: GitHub Pull Request #3533