[
https://issues.apache.org/jira/browse/PIG-3979?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Rohini Palaniswamy updated PIG-3979:
------------------------------------
Attachment: PIG-3979-5.patch
Attached patch hopefully fixes all those issues. I also reverted back to using
num records for samples as it was hitting default threshold of 20K records and
aggregating and spilling couple of times well in advance before sample size was
reached when I ran some modified tests on bigdata.conf. I made the spill()
estimateThresholds() so that should solve the problem the sampleSize check was
put in. Also it avoids the penalty of collecting the sample size in advance
when it might not actually be needed if sizeReduction factor was not met.
Review board link - https://reviews.apache.org/r/27169/
> group all performance, garbage collection, and incremental aggregation
> ----------------------------------------------------------------------
>
> Key: PIG-3979
> URL: https://issues.apache.org/jira/browse/PIG-3979
> Project: Pig
> Issue Type: Improvement
> Components: impl
> Affects Versions: 0.12.0, 0.11.1
> Reporter: David Dreyfus
> Assignee: David Dreyfus
> Fix For: 0.14.0
>
> Attachments: PIG-3979-3.patch, PIG-3979-4.patch, PIG-3979-5.patch,
> PIG-3979-synchronous-spill.patch, PIG-3979-v1.patch, POPartialAgg.java.patch,
> SpillableMemoryManager.java.patch
>
>
> I have a PIG statement similar to:
> summary = foreach (group data ALL) generate
> COUNT(data.col1), SUM(data.col2), SUM(data.col2)
> , Moments(col3)
> , Moments(data.col4)
> There are a couple of hundred columns.
> I set the following:
> SET pig.exec.mapPartAgg true;
> SET pig.exec.mapPartAgg.minReduction 3;
> SET pig.cachedbag.memusage 0.05;
> I found that when I ran this on a JVM with insufficient memory, the process
> eventually timed out because of an infinite garbage collection loop.
> The problem was invariant to the memusage setting.
> I solved the problem by making changes to:
> org.apache.pig.backend.hadoop.executionengine.physicalLayer.relationalOperator.POPartialAgg.java
> Rather than reading in 10000 records to establish an estimate of the
> reduction, I make an estimate after reading in enough tuples to fill
> pig.cachedbag.memusage percent of Runtime.getRuntime().maxMemory().
> I also made a change to guarantee at least one record allowed in second tier
> storage. In the current implementation, if the reduction is very high 1000:1,
> space in second tier storage is zero.
> With these changes, I can summarize large data sets with small JVMs. I also
> find that setting pig.cachedbag.memusage to a small number such as 0.05
> results in much better garbage collection performance without reducing
> throughput. I suppose tuning GC would also solve a problem with excessive
> garbage collection.
> The performance is sweet.
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
