On 4/18/19 2:14 AM, Andreas Kretschmer wrote:
Am 18.04.19 um 08:52 schrieb rihad:
Hi. Say there are 2 indexes:
"foo_index" btree (foo_id)
"multi_index" btree (foo_id, approved, expires_at)
foo_id is an integer. Some queries involve all three columns in
their WHERE clauses, some involve only foo_id.
Would it be ok from general performance standpoint to remove
foo_index and rely only on multi_index? I know that
PG would have to do less work updating just one index compared
to updating them both, but wouldn't searches
on foo_id alone become slower?
it depends .
it depends on the queries you are using, on your workload. a
multi-column-index will be large than an index over just one
column,
therefore you will have more disk-io when you read from such an
index.
But two indexes are larger than one index, and updating two indexes
requires more disk IO than updating one index.
(Prefix compression would obviate the need for this question. Then
your multi-column index would be much smaller.)
--
Angular momentum makes the world go 'round.
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