Re: indexing timestamp fields

teknokrat <teknokrat(at)yahoo(dot)com> writes:
> Christopher Browne wrote:
>
>> teknokrat <teknokrat(at)yahoo(dot)com> writes:
>>
>>>Is it a good idea to index timestamp fields? what about date fields in
>>>general?
>> If you need to order by a timestamp, then it can be worthwhile.
>> If that timestamp can be null, and is rarely populated, then you
>> might
>> get a _big_ benefit from creating a partial index as with:
>> create index by_some_date on my_table(some_date) where some_date is
>> not null;
>
> I have a lot of queries of the " where timestamp < some date " type
> and was wondering if an index would improve performance. None of the
> timestamps are null and they are always populated

There isn't a single straight answer on this.
It _might_ help; it might not.

- It might be that adding "timestamp" to some existing index would be
better still.

- If the table is real big, and the "ts < other_ts" doesn't restrict
things very much, then you may merely sit in between an index scan
that touches every page of the table and a Seq Scan that does the
same.

Try creating the index, and do some EXPLAIN ANALYZE queries to see
what happens; that should give you an idea as to how effective this
is.
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Christopher Browne
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