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https://issues.apache.org/jira/browse/CASSANDRA-4032?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13226166#comment-13226166
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Peter Schuller edited comment on CASSANDRA-4032 at 3/9/12 4:05 PM:
-------------------------------------------------------------------
{quote}
Are we sure that what we want is a SynchronousQueue with task rejected? After
all, there is only on global memoryMeter, so we could end up failing to
updateLiveRatio just based on a race, even if calculations are fast. I'd
suggest instead a bounded queue (but maybe not infinite and we could indeed
just skip task if that queue gets full).
{quote}
I agree it's fishy, though I'd suggest a separate ticket. This patch is
intended to make the code behave the way the original commit intended.
This (from the code, not my patch) seems legit though:
{code}
// we're careful to only allow one count to run at a time because counting
is slow
// (can be minutes, for a large memtable and a busy server), so we could
keep memtables
// alive after they're flushed and would otherwise be GC'd.
{code}
We could have one queue per unique CF and have a consumer that iterates over
the set of queues, guaranteeing that each CF gets processed once per "cycle". A
simpler solution is probably preferable though if we can think of one.
was (Author: scode):
{code}
Are we sure that what we want is a SynchronousQueue with task rejected? After
all, there is only on global memoryMeter, so we could end up failing to
updateLiveRatio just based on a race, even if calculations are fast. I'd
suggest instead a bounded queue (but maybe not infinite and we could indeed
just skip task if that queue gets full).
{code}
I agree it's fishy, though I'd suggest a separate ticket. This patch is
intended to make the code behave the way the original commit intended.
This (from the code, not my patch) seems legit though:
{code}
// we're careful to only allow one count to run at a time because counting
is slow
// (can be minutes, for a large memtable and a busy server), so we could
keep memtables
// alive after they're flushed and would otherwise be GC'd.
{code}
We could have one queue per unique CF and have a consumer that iterates over
the set of queues, guaranteeing that each CF gets processed once per "cycle". A
simpler solution is probably preferable though if we can think of one.
> memtable.updateLiveRatio() is blocking, causing insane latencies for writes
> ---------------------------------------------------------------------------
>
> Key: CASSANDRA-4032
> URL: https://issues.apache.org/jira/browse/CASSANDRA-4032
> Project: Cassandra
> Issue Type: Bug
> Components: Core
> Reporter: Peter Schuller
> Assignee: Peter Schuller
> Fix For: 1.1.0
>
> Attachments: CASSANDRA-4032-1.1.0-v1.txt
>
>
> Reproduce by just starting a fresh cassandra with a heap large enough for
> live ratio calculation (which is {{O(n)}}) to be insanely slow, and then
> running {{./bin/stress -d host -n100000000 -t10}}. With a large enough heap
> and default flushing behavior this is bad enough that stress gets timeouts.
> Example ("blocked for" is my debug log added around submit()):
> {code}
> INFO [MemoryMeter:1] 2012-03-09 15:07:30,857 Memtable.java (line 198)
> CFS(Keyspace='Keyspace1', ColumnFamily='Standard1') liveRatio is
> 8.89014894083727 (just-counted was 8.89014894083727). calculation took
> 28273ms for 1320245 columns
> WARN [MutationStage:8] 2012-03-09 15:07:30,857 Memtable.java (line 209)
> submit() blocked for: 231135
> {code}
> The calling code was written assuming a RejectedExecutionException is thrown,
> but it's not because {{DebuggableThreadPoolExecutor}} installs a blocking
> rejection handler.
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