[CASSANDRA-8459] "autocompaction" on reads can prevent memtable space reclaimation

• Type: Bug
• Status: Resolved
• Priority: Normal
• Resolution: Fixed
• Fix Version/s: 2.1.3
• Severity: Normal
• Assignee: Benedict Elliott Smith
• Reporter: Benedict Elliott Smith

Authors

Benedict Elliott Smith

• Created: 11/Dec/14 13:13
• Updated: 16/Apr/19 09:31
• Resolved: 12/Dec/14 13:17

Description

Memtable memory reclamation is dependent on reads always making progress, however on the collectTimeOrderedData critical path it is possible for the read to perform a write inline, and for this write to block waiting for memtable space to be reclaimed. However the reclaimation is blocked waiting for this read to complete.

There are a number of solutions to this, but the simplest is to make the defragmentation happen asynchronously, so the read terminates normally.