[HBASE-10227] When a region is opened, its mvcc isn't correctly recovered when there are split hlogs to replay

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Abandoned
• Component/s: regionserver
• Assignee: Unassigned
• Reporter: Honghua Feng
• Created: 23/Dec/13 10:21
• Updated: 17/Jun/22 15:34
• Resolved: 17/Jun/22 15:33

Description

When opening a region, all stores are examined to get the max MemstoreTS and it's used as the initial mvcc for the region, and then split hlogs are replayed. In fact the edits in split hlogs have kvs with greater mvcc than all MemstoreTS in all store files, but replaying them don't increment the mvcc according at all. From an overall perspective this mvcc recovering is 'logically' incorrect/incomplete.

Why currently it doesn't incur problem is because no active scanners exists and no new scanners can be created before the region opening completes, so the mvcc of all kvs in the resulted hfiles from hlog replaying can be safely set to zero. They are just treated as kvs put 'earlier' than the ones in HFiles with mvcc greater than zero(say 'earlier' since they have mvcc less than the ones with non-zero mvcc, but in fact they are put 'later'), and without any incorrect impact just because during region opening there are no active scanners existing / created.

This bug is just in 'logic' sense for the time being, but if later on we need to survive mvcc in the region's whole logic lifecycle(across regionservers) and never set them to zero, this bug needs to be fixed first.

Issue Links

• contains: HBASE-10243 store mvcc in WAL
• is depended upon by: HBASE-10241 implement mvcc-consistent scanners (across recovery)
• is related to: HBASE-10243 store mvcc in WAL