Re: Speed up Clog Access by increasing CLOG buffers

Here is the performance data (configuration of machine used to perform this test is mentioned at end of mail):

median of 3, 20-min pgbench tpc-b results for --unlogged-tables

 

I am not exactly sure why using content lock (defined USE_CONTENT_LOCK in 0003-Use-a-much-more-granular-locking-model-for-the-clog-) patch or no content lock (not defined USE_CONTENT_LOCK) patch gives poor performance at 128 client, may it is due to some bug in patch or due to some reason mentioned by Robert [1] (usage of two locks instead of one).  On running it many-2 times with content lock and no content lock patch, some times it gives 80 ~ 81K TPS at 128 client count which is approximately 3% higher than group_clog_v8 patch which indicates that group clog approach is able to address most of the remaining contention (after increasing clog buffers) around CLOGControlLock.  There is one small regression observed with no content lock patch at lower client count (2) which might be due to run-to-run variation or may be it is due to increased number of instructions due to atomic ops, need to be investigated if we want to follow no content lock approach.

Note, I have not posted TPS numbers with HEAD, as I have already shown above that increasing clog bufs has increased TPS from ~36K to ~68K at 128 client-count.