[jira] [Updated] (PIG-3956) UDF profile is often misleading

["Cheolsoo Park (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/PIG-3956?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Cheolsoo Park updated PIG-3956:
-------------------------------

    Attachment: PIG-3956-1.patch

The attached patch makes the frequency of profiling configurable. The default is 100, so the default behavior remains the same.

I also updated {{conf/pig.properties}} and the performance page in Pig manual.

> UDF profile is often misleading
> -------------------------------
>
>                 Key: PIG-3956
>                 URL: https://issues.apache.org/jira/browse/PIG-3956
>             Project: Pig
>          Issue Type: Bug
>          Components: impl
>            Reporter: Cheolsoo Park
>             Fix For: 0.14.0
>
>         Attachments: PIG-3956-1.patch
>
>
> Pig provides UDF profiling via the {{pig.udf.profile}} perperty. How it works is that it samples every 100th UDF invocation and increments a counter by 100 x elapsed time.
> {code}
> private final static int TIMING_FREQ = 100;
> ...
> PigStatusReporter.getInstance().incrCounter(counterGroup, TIMING_COUNTER,
>     Math.round((System.nanoTime() - startNanos) / 1000) * TIMING_FREQ);
> {code}
> The problem is that this assumes every invocation takes about the same time, which doesn't hold true oftentimes.
> Here is an example. TIMING_FREQ = 100.
> {code}
> set pig.udf.profile true;
> set opt.fetch false;
> l = LOAD 'foo' AS (value:chararray);
> f = FOREACH l GENERATE LOWER(value);
> DUMP f;
> {code}
> This job gives me the following counters-
> {code}
> org.apache.pig.builtin.LOWER - approx_invocations: 6,144,600
> org.apache.pig.builtin.LOWER - approx_microsecs: 130,913,800
> {code}
> However, if I change TIMING_FREQ to 1, I get the followings-
> {code}
> org.apache.pig.builtin.LOWER - approx_invocations: 6,144,248
> org.apache.pig.builtin.LOWER - approx_microsecs: 19,711,842
> {code}
> As can be seen, approx_microsecs is 6x larger when sampling every 100th invocation as compared to when sampling every invocation.



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