Re: [REVIEW] Re: Compression of full-page-writes

>I will repeat the above tests with high load on CPU and using the benchmark
given by Fujii-san and post the results.

Average % of CPU usage at user level for each of the compression algorithm
are as follows.

Compression        Multiple            Single

Off                        81.1338            81.1267
LZ4                      81.0998            81.1695
Snappy:                80.9741             80.9703
Pglz :                    81.2353            81.2753

<http://postgresql.1045698.n5.nabble.com/file/n5818552/CPU_utilization_user_single.png>
<http://postgresql.1045698.n5.nabble.com/file/n5818552/CPU_utilization_user.png>

The numbers show CPU utilization of Snappy is the least. The CPU utilization
in increasing order is
pglz > No compression > LZ4 > Snappy

The variance of average CPU utilization numbers is very low. However ,
snappy seems to be best when it comes to lesser utilization of CPU.

As per the measurement results posted till date

LZ4 outperforms snappy and pglz in terms of compression ratio and
performance. However , CPU utilization numbers show snappy utilizes least
amount of CPU . Difference is not much though.

As there has been no consensus yet about which compression algorithm to
adopt, is it better to make this decision independent of the FPW compression
patch as suggested earlier in this thread?. FPW compression can be done
using built in compression pglz as it shows considerable performance over
uncompressed WAL and good compression ratio
Also, the patch to compress multiple blocks at once gives better compression
as compared to single block. ISTM that performance overhead introduced by
multiple blocks compression is slightly higher than single block compression
which can be tested again after modifying the patch to use pglz .  Hence,
this patch can be built using multiple blocks compression.

Thoughts?



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