Re: Slow Bitmap Index Scan

Upon further analysis, this is - unsurprisingly - taking place when we have multiple prefixed search terms in a ts_query going against a tsvector index.

We have roughly 30 million rows in the table, and the search column is basically a concatenation of a location's name (think "Walmart #123456") and its street address.

We use these searches mostly for autocompleting of a location search. So the search for that record above might be "Walmart 123", which we change to be to_tsquery('walmart:* &123:*'). We prefix both terms to correct for misspellings or lazy typing.

Is it unrealistic to think that we could have sub-1000ms searches against that size of a table?

On 11/28/18, 2:18 PM, "Justin Pryzby" <pryzby(at)telsasoft(dot)com> wrote:

On Wed, Nov 28, 2018 at 07:08:53PM +0000, Scott Rankin wrote:
> We recently moved our production database systems from a 9.4 running on a self-managed EC2 instance to 9.6.10 on Amazon’s AWS (same RAM, CPU). After the move, we’re finding that certain queries that we run against a GIN full-text index have some occasionally very slow executions and I’m struggling to figure out what to do about it. I would be very grateful for any ideas!
>
> The setup we have is a 32-core, 244 GB RAM primary with a same-sized read replica. The queries are running off the replica, but performance is roughly the same between the master and the replica.
>
> Here’s a query that’s performing badly:

Can you compare or show the explain(analyze,buffers) for a fast query instance
vs slow query instance ? Is it slower due to index access or heap? Due to
cache misses ?

Also, you have big ram - have you tried disabling KSM or THP ?
https://www.postgresql.org/message-id/20170718180152.GE17566%40telsasoft.com

Justin

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