Any rule of the thumb with which number of pages per relation it is worth to start indexing ?
The code for the monitoring tool check_postgres uses table size larger than 5.12kb as a rule of thumb, expecting that for tables smaller than 5.12kb the planner may choose a sequential scan instead because the table is so small. check_postgres was written a long time ago though, so someone who is more familiar with the optimizer may be able to provide a better estimate.
>On 7/9/2015 12:41 PM, Tom Lane wrote: >> Andy Colson <andy@squeakycode.net> writes: >>> My question is: Will PG cache only the index (assuming it can always do >>> an Index Only Scan), or will it cache the table as well?
I'm not sure that indexes on tiny tables are useful. They raise the options to consider by the query planner, which has its small cost too. I'd be interested on other opinions on this. Any rule of the thumb with which number of pages per relation it is worth to start indexing ?
And still another question: I've have tiny static tables too, that never got analyzed. Can this fool the query planner in a negative way ?