Fuud created CASSANDRA-13444:
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Summary: Fast and garbage-free Streaming Histogram
Key: CASSANDRA-13444
URL: https://issues.apache.org/jira/browse/CASSANDRA-13444
Project: Cassandra
Issue Type: Improvement
Components: Compaction
Reporter: Fuud
StreamingHistogram is cause of high cpu usage and GC pressure.
It was improved at CASSANDRA-13038 by introducing intermediate buffer to try
accumulate different values into the big map before merging them into smaller
one.
But there was not enought for TTL's distributed within large time. Rounding
(also introduced at 13038) can help but it reduce histogram precision specially
in case where TTL's does not distributed uniformly.
There are several improvements that can help to reduce cpu and gc usage. Them
all included in the pool-request as separate revisions thus you can test them
independently.
Improvements list:
# Use Map.computeIfAbsent instead of get->checkIfNull->put chain. In this way
"add-or-accumulate" operation takes one map operation instead of two. But this
method (default-defined in interface Map) is overriden in HashMap but not in
TreeMap. Thus I changed spool type to HashMap.
# As we round incoming values to _roundSeconds_ we can also round value on
merge. It will enlarge hit rate for bin operations.
# Because we inserted only integers into Histogram and rounding values to
integers we can use *int* type everywhere.
# Histogram takes huge amount of time merging values. In merge method largest
amount of time taken by finding nearest points. It can be eliminated by holding
additional TreeSet with differences, sorted from smalest to greatest.
# Because we know max size of _bin_ and _differences_ maps we can replace them
with sorted arrays. Search can be done with _Arrays.binarySearch_ and
insertion/deletions can be done by _System.arraycopy_. Also it helps to merge
some operations into one.
# Because spool map is also limited we can replace it with open address
primitive map. It's finaly reduce allocation rate to zero.
You can see gain given by each step in the attached file. First number is time
for one benchmark invocation and second - is allocation rate in Mb per
operation.
Overall gain:
|.|.|Payload/SpoolSize|.|.|.|% from original
|.|.|.|original|.|optimized|
|.|.|secondInMonth/0|.|.|.|
|time ms/op|.|.|10747,684|.|5545,063|51,6
|allocation Mb/op|.|.|2441,38858|.|0,002105713|0
|.|.|.|.|.|.|
|.|.|secondInMonth/1000|.|.|.|
|time ms/op|.|.|8988,578|.|5791,179|64,4
|allocation Mb/op|.|.|2440,951141|.|0,017715454|0
|.|.|.|.|.|.|
|.|.|secondInMonth/10000|.|.|.|
|time ms/op|.|.|10711,671|.|5765,243|53,8
|allocation Mb/op|.|.|2437,022537|.|0,264083862|0
|.|.|.|.|.|.|
|.|.|secondInMonth/100000|.|.|.|
|time ms/op|.|.|13001,841|.|5638,069|43,4
|allocation Mb/op|.|.|2396,947113|.|2,003662109|0,1
|.|.|.|.|.|.|
|.|.|secondInDay/0|.|.|.|
|time ms/op|.|.|10381,833|.|5497,804|53
|allocation Mb/op|.|.|2441,166107|.|0,002105713|0
|.|.|.|.|.|.|
|.|.|secondInDay/1000|.|.|.|
|time ms/op|.|.|8522,157|.|5929,871|69,6
|allocation Mb/op|.|.|1973,112381|.|0,017715454|0
|.|.|.|.|.|.|
|.|.|secondInDay/10000|.|.|.|
|time ms/op|.|.|10234,978|.|5480,077|53,5
|allocation Mb/op|.|.|2306,057404|.|0,262969971|0
|.|.|.|.|.|.|
|.|.|secondInDay/100000|.|.|.|
|time ms/op|.|.|2971,178|.|139,079|4,7
|allocation Mb/op|.|.|172,1276245|.|2,001721191|1,2
|.|.|.|.|.|.|
|.|.|secondIn3Hour/0|.|.|.|
|time ms/op|.|.|10663,123|.|5605,672|52,6
|allocation Mb/op|.|.|2439,456818|.|0,002105713|0
|.|.|.|.|.|.|
|.|.|secondIn3Hour/1000|.|.|.|
|time ms/op|.|.|9029,788|.|5838,618|64,7
|allocation Mb/op|.|.|2331,839249|.|0,180664063|0
|.|.|.|.|.|.|
|.|.|secondIn3Hour/10000|.|.|.|
|time ms/op|.|.|4862,409|.|89,001|1,8
|allocation Mb/op|.|.|965,4871887|.|0,251711652|0
|.|.|.|.|.|.|
|.|.|secondIn3Hour/100000|.|.|.|
|time ms/op|.|.|1484,454|.|95,044|6,4
|allocation Mb/op|.|.|153,2464722|.|2,001712809|1,3
|.|.|.|.|.|.|
|.|.|secondInMin/0|.|.|.|
|time ms/op|.|.|875,118|.|424,11|48,5
|allocation Mb/op|.|.|610,3554993|.|0,001776123|0
|.|.|.|.|.|.|
|.|.|secondInMin/1000|.|.|.|
|time ms/op|.|.|568,7|.|84,208|14,8
|allocation Mb/op|.|.|0,007598114|.|0,01810023|238,2
|.|.|.|.|.|.|
|.|.|secondInMin/10000|.|.|.|
|time ms/op|.|.|573,595|.|83,862|14,6
|allocation Mb/op|.|.|0,007597351|.|0,252473872|3323,2
|.|.|.|.|.|.|
|.|.|secondInMin/100000|.|.|.|
|time ms/op|.|.|584,457|.|86,554|14,8
|allocation Mb/op|.|.|0,007595825|.|2,002506106|26363,2
You may notice increased allocation rate for secondInMin payload. It is because
test use small values and Integer.valueOf use cache for them. In real case
where incoming values will be timestamps this cache will not work. Also
constant memory 2 Mb per StreamingHistogram is quite good.
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