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
