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https://issues.apache.org/jira/browse/CASSANDRA-4681?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Oleg Kibirev updated CASSANDRA-4681:
------------------------------------
Description:
When profiling high volume inserts into Cassandra running on a host with fast
SSD and CPU, Thread.yield() invoked by SlabAllocator appeared as the top item
in CPU samples. The fix is to return a regular byte buffer if current slab is
being initialized by another thread. So instead of:
if (oldOffset == UNINITIALIZED)
{
// The region doesn't have its data allocated yet.
// Since we found this in currentRegion, we know that
whoever
// CAS-ed it there is allocating it right now. So spin-loop
// shouldn't spin long!
Thread.yield();
continue;
}
do:
if (oldOffset == UNINITIALIZED)
return ByteBuffer.allocate(size);
I achieved 4x speed up in my (admittedly specialized) benchmark by using an
optimized version of SlabAllocator attached. Since this code is in the critical
path, even doing excessive atomic instructions or allocated unneeded ByteBuffer
instances has a measurable effect on performance
was:
When profiling high volume inserts into Cassandra running on a host with fast
SSD and CPU, Thread.yield() invoked by SlabAllocator appeared as the top item
in CPU samples. The fix is to return a regular byte buffer if current slab is
being initialized by another thread. So instead of:
if (oldOffset == UNINITIALIZED)
{
// The region doesn't have its data allocated yet.
// Since we found this in currentRegion, we know that
whoever
// CAS-ed it there is allocating it right now. So spin-loop
// shouldn't spin long!
Thread.yield();
continue;
}
do:
if (oldOffset == UNINITIALIZED)
return ByteBuffer.allocate(size);
I achieved 4x speed up in my (admittedly specialized) benchmark.
> SlabAllocator spends a lot of time in Thread.yield
> --------------------------------------------------
>
> Key: CASSANDRA-4681
> URL: https://issues.apache.org/jira/browse/CASSANDRA-4681
> Project: Cassandra
> Issue Type: Bug
> Components: Core
> Affects Versions: 1.1.5
> Environment: OEL Linux
> Reporter: Oleg Kibirev
>
> When profiling high volume inserts into Cassandra running on a host with fast
> SSD and CPU, Thread.yield() invoked by SlabAllocator appeared as the top item
> in CPU samples. The fix is to return a regular byte buffer if current slab is
> being initialized by another thread. So instead of:
> if (oldOffset == UNINITIALIZED)
> {
> // The region doesn't have its data allocated yet.
> // Since we found this in currentRegion, we know that
> whoever
> // CAS-ed it there is allocating it right now. So
> spin-loop
> // shouldn't spin long!
> Thread.yield();
> continue;
> }
> do:
> if (oldOffset == UNINITIALIZED)
> return ByteBuffer.allocate(size);
> I achieved 4x speed up in my (admittedly specialized) benchmark by using an
> optimized version of SlabAllocator attached. Since this code is in the
> critical path, even doing excessive atomic instructions or allocated unneeded
> ByteBuffer instances has a measurable effect on performance
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