Sam Tunnicliffe created CASSANDRA-11159:
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Summary: SASI indexes don't switch memtable on flush
Key: CASSANDRA-11159
URL: https://issues.apache.org/jira/browse/CASSANDRA-11159
Project: Cassandra
Issue Type: Bug
Components: Local Write-Read Paths
Reporter: Sam Tunnicliffe
Assignee: Sam Tunnicliffe
Priority: Critical
Fix For: 3.4
SASI maintains its own in-memory structures for indexing the contents of a base
Memtable. On flush, these are simply discarded & replaced with an new instance,
whilst the on disk index is built as the base memtable is flushed to SSTables.
SASIIndex implements INotificationHandler and this switching of the index
memtable is triggered by receipt of a MemtableRenewedNotification. In the
original SASI implementation, one of the necessary modifications to C* was to
emit this notification from DataTracker::switchMemtable, but this was
overlooked when porting to 3.0. The net result is that the index memtable is
never switched out, which eventually leads to OOME.
Simply applying the original modification isn't entirely appropriate though, as
it creates a window where it's possible for the index memtable to have been
switched, but the flushwriter is yet to finish writing the new index sstables.
During this window, index entries will be missing and query results inaccurate.
I propose leaving Tracker::switchMemtable as is, so that INotificationConsumers
are only notified from there when truncating, but adding similar notifications
in Tracker::replaceFlushed, to fire after the View is updated.
I'm leaning toward re-using MemtableRenewedNotification for this as
semantically I don't believe there's any meaningful difference between the
flush and truncation cases here. If anyone has a compelling argument for a new
notification type though to distinguish the two events, I'm open to hear it.
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