[
https://issues.apache.org/jira/browse/CASSANDRA-1954?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12995091#comment-12995091
]
Stu Hood commented on CASSANDRA-1954:
-------------------------------------
An idea to replace this lock was proposed in IRC yesterday: if the list of
memtables and sstables was stored in a single immutable, cas'able structure,
you could atomically swap a memtable from active to flushing, and then from
flushing into an sstable. Example structure:
{code:java}class View {
final List<Memtable> active;
final List<Memtable> flushing;
final List<SSTableReader> sstables;
}{code}
So a writing thread noticing an active Memtable past its threshold would
attempt to CAS in a new Memtable while moving the current memtable to flushing.
A thread finishing a flush would attempt to CAS the memtable it flushed out of
flushing and into the sstable list.
> Double-check or replace RRW memtable lock
> -----------------------------------------
>
> Key: CASSANDRA-1954
> URL: https://issues.apache.org/jira/browse/CASSANDRA-1954
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Reporter: Stu Hood
> Priority: Minor
> Attachments:
> 0001-Double-check-in-maybeSwitchMemtable-to-minimize-writeL.txt
>
>
> {quote}...when a Memtable reaches its threshold, up to (all) N write threads
> will often notice, and race to acquire the writeLock in order to freeze the
> memtable. This means that we do way more writeLock acquisitions than we need
> to...{quote}
> See CASSANDRA-1930 for backstory, but adding double checking inside a read
> lock before trying to re-entrantly acquire the writelock would eliminate most
> of these excess writelock acquisitions.
> Alternatively, we should explore removing locking from these structures
> entirely, and replacing the writeLock acquisition with a per-memtable counter
> of active threads.
--
This message is automatically generated by JIRA.
-
For more information on JIRA, see: http://www.atlassian.com/software/jira
