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From Jean-Daniel Cryans <jdcry...@apache.org>
Subject Re: Early comparisons between 0.90 and 0.92
Date Tue, 20 Dec 2011 00:43:28 GMT
I redid the tests with a 64KB block size and went all the way to
testing HFileV2 (which was badly missing).

Scans:

0.90: Bursts up to 1.7M
0.92 V1: Bursts up to 1.4M
0.92 V2: Bursts up to 1.8M

Random reads:

0.90: Steady at 165k
0.92 V1: Steady at 195k
0.92 V2: Steady at 245k

Basically, as long as people migrate to HFileV2 there won't be any problems.

I attached a profiler to see what was going on with scans and it seems
that 0.92 V1 uses a different path than both 0.90 and 0.92 V2. After
testing V2, I think it's not necessary to dig further into the issue
although it seems to be related to the usage of BufferedInputStream in
the faster paths.

Sorry for the original scare, hopefully this is useful for someone.

J-D

On Wed, Dec 14, 2011 at 5:26 PM, Jean-Daniel Cryans <jdcryans@apache.org> wrote:
> Hey guys,
>
> I was doing some comparisons between 0.90.5 and 0.92.0, mainly
> regarding reads. The numbers are kinda irrelevant but the differences
> are. BTW this is on CDH3u3 with random reads.
>
> In 0.90.0, scanning 50M rows that are in the OS cache I go up to about
> 1.7M rows scanned per second.
>
> In 0.92.0, scanning those same rows (meaning that I didn't run
> compactions after migrating so it's picking the same data from the OS
> cache), I scan about 1.1 rows per second.
>
> 0.92 is 50% slower when scanning.
>
> In 0.90.0 random reading 50M rows that are OS cached I can do about
> 200k reads per second.
>
> In 0.92.0, again with those same rows, I can go up to 260k per second.
>
> 0.92 is 30% faster when random reading.
>
> I've been playing with that data set for a while and the numbers in
> 0.92.0 when using HFileV1 or V2 are pretty much the same meaning that
> something else changed or the code that's generic to both did.
>
>
> I'd like to be able to associate those differences to code changes in
> order to understand what's going on. I would really appreciate if
> others also took some time to test it out or to think about what could
> cause this.
>
> Thx,
>
> J-D

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