I do have a performance problem, and it is due to I/O bottleneck. We don't have pg_stat_statements installed, we will check it out. Thanks
On Mon, Sep 30, 2013 at 8:44 PM, Jeff Janes <jeff.ja...@gmail.com> wrote: > On Mon, Sep 30, 2013 at 5:45 AM, Xenofon Papadopoulos <xpa...@gmail.com>wrote: > >> I am trying to understand the heap_blks_read and heap_blks_hit of >> pg_statio_all_tables in 9.2 >> Do the numbers refer only to SELECT, or they take INSERT into account? >> > > They take insert (and update, and delete) into account. > > >> Would a heap_blks_read / ( heap_blks_read + heap_blks_hit ) ration of >> over 55% combined with a heap_blks_read value of over 50M indicate an issue >> with the queries affecting that table, or it is normal if the table is >> heavily written to? >> > > There is really no answer to that. For one thing, some unknown number of > those heap_blks_read are really coming from the OS/FS's page cache, not > from disk. For another thing, we don't know how many queries, of what > kind, on how large of a table, those 50M reads are supporting. > > Do you have a performance problem? If so, is it due to IO bottleneck? If > so, high heap_blks_read on a certain table might indicate where the problem > could be (although pg_stat_statements would probably do a better job). > > In the absence of a specific problem to be diagnosed, those numbers don't > mean very much. > > > Cheers, > > Jeff >
