Re: Index only scan sometimes switches to sequential scan for small amount of rows

Hi, thanks for having a look and thinking with us

On 25 March 2015 at 13:45, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> wrote:
> Can you post results for this query?
>
> SELECT stats, COUNT(*) FROM print_list group by 1

status | count
----------------+---------
ERROR | 159
PREPARED | 10162
PRINTED | 3551367
TO_BE_PREPARED | 2
(4 rows)

>> We can also increase the 'Stats target' for this table, which will
>> cause the statistics to contain information about 'NOT_YET_PRINTED'
>> more often, but even then, it may not find any of these records, as
>> they sometimes do not exist.
>
> This is a better solution, IMHO.

We'll have a go at this, also if what you say about values having to
appear at least twice, the other values may make it into
most_common_*, which would make it clearer to us.

We're a bit hesitant to decrease random_page_cost (currently 3 in this
cluster) as a lot more is happening on this database.