Queue table that quickly grows causes query planner to choose poor plan

Hi All,

I’m having performance trouble with a particular set of queries. It goes a bit like this

1) queue table is initially empty, and very narrow (1 bigint column)
2) we insert ~30 million rows into queue table
3) we do a join with queue table to delete from another table (delete from a using queue where a.id<http://a.id> = queue.id<http://queue.id>), but postgres stats say that queue table is empty, so it uses a nested loop over all 30 million rows, taking forever

If I kill the query in 3 and let it run again after autoanalyze has done it’s thing then it is very quick

This queue table is empty 99% of the time, and the query in 3 runs immediately after step 2. Is there any likelyhood that tweaking the autoanalyze params would help in this case? I don’t want to explicitly analyze the table between steps 2 and three either as there are other patterns of use where for example 0 rows are inserted in step 2 and this is expected to run very very quickly. Do I have any other options?

Postgres 9.5 ATM, but an upgrade is in planning.

Thanks in advance

David Wheeler
Software developer

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