Postgres is eating the database world
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Postgres is eating the database world
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Re: Postgres is eating the database world
#2Postgres is simply the best. One thing I would like however is the ability to have control over the query planner for specific tasks. There is a dark art to influencing the query planner, but essentially it is unpredictable, and postgres can get it consistently wrong in certain scenarios. If you could just enable a special query mode that gives you absolute control over the QP for that query, it would solve a major pain point.
I'm not a database developer, and last time I researched this (a few years ago) I found many good reasons for not enabling this from postgres contributors. But it would still be very useful.
Re: Postgres is eating the database world
#3Postgres is simply the best. One thing I would like however is the ability to have control over the query planner for specific tasks. There is a dark art to influencing the query planner, but essentially it is unpredictable, and postgres can get it consistently wrong in certain scenarios. If you could just enable a special query mode that gives you absolute control over the QP for that query, it would solve a major p…
I’m currently learning the basics of this. Currently struggling with multiple similar scenarios where switching from a left to an inner join, or any equivalent, kills performance. But these are aggregation queries so there are only 5 records returned. I could just filter in my app code no problem. But why the hell does adding “where foo.id is not null” in SQL make it O(N*M)??? CTEs are not helping.
Re: Postgres is eating the database world
#4Postgres is simply the best. One thing I would like however is the ability to have control over the query planner for specific tasks. There is a dark art to influencing the query planner, but essentially it is unpredictable, and postgres can get it consistently wrong in certain scenarios. If you could just enable a special query mode that gives you absolute control over the QP for that query, it would solve a major p…
I haven’t used Postgres but is this the issue you’re talking about? https://github.com/launchbadge/sqlx/pull/1539
Re: Postgres is eating the database world
#5Postgres is simply the best. One thing I would like however is the ability to have control over the query planner for specific tasks. There is a dark art to influencing the query planner, but essentially it is unpredictable, and postgres can get it consistently wrong in certain scenarios. If you could just enable a special query mode that gives you absolute control over the QP for that query, it would solve a major p…
I haven’t used Postgres but is this the issue you’re talking about? https://github.com/launchbadge/sqlx/pull/1539
No this is a fundamental concept in postgres. If you do EXPLAIN ANALYZE on a query, you get the query plan, which is influenced by the query, indexes, table structure, etc. But the QP may decide to do a silly thing like a sequential scan where a better path exists, and adding an index to avoid the scan would be cost prohibitive. So if you could just override the QP and say "Use this index and do this type of sort and then this type of scan, damn the consequences!" it would give the query writer full control. I don't understand why you can't just force the system to follow a path - you as the developer pay for it regardless.
Re: Postgres is eating the database world
#6Postgres is simply the best. One thing I would like however is the ability to have control over the query planner for specific tasks. There is a dark art to influencing the query planner, but essentially it is unpredictable, and postgres can get it consistently wrong in certain scenarios. If you could just enable a special query mode that gives you absolute control over the QP for that query, it would solve a major p…
pg_hint_plan —— Give PostgreSQL ability to manually force some decisions in execution plans. https://github.com/ossc-db/pg_hint_plan
Re: Postgres is eating the database world
#7Postgres is simply the best. One thing I would like however is the ability to have control over the query planner for specific tasks. There is a dark art to influencing the query planner, but essentially it is unpredictable, and postgres can get it consistently wrong in certain scenarios. If you could just enable a special query mode that gives you absolute control over the QP for that query, it would solve a major p…
I’m currently learning the basics of this. Currently struggling with multiple similar scenarios where switching from a left to an inner join, or any equivalent, kills performance. But these are aggregation queries so there are only 5 records returned. I could just filter in my app code no problem. But why the hell does adding “where foo.id is not null” in SQL make it O(N*M)??? CTEs are not helping.
Have you checked with EXPLAIN ANALYZE VERBOSE?
Re: Postgres is eating the database world
#8Earlier quoted context omitted.
I haven’t used Postgres but is this the issue you’re talking about? https://github.com/launchbadge/sqlx/pull/1539
No this is a fundamental concept in postgres. If you do EXPLAIN ANALYZE on a query, you get the query plan, which is influenced by the query, indexes, table structure, etc. But the QP may decide to do a silly thing like a sequential scan where a better path exists, and adding an index to avoid the scan would be cost prohibitive. So if you could just override the QP and say "Use this index and do this type of sort and…
I wonder if for non-trivial use cases we should just go back to imperative programming.
Re: Postgres is eating the database world
#9Postgres is simply the best. One thing I would like however is the ability to have control over the query planner for specific tasks. There is a dark art to influencing the query planner, but essentially it is unpredictable, and postgres can get it consistently wrong in certain scenarios. If you could just enable a special query mode that gives you absolute control over the QP for that query, it would solve a major p…
MySQL offers this via use/force index (…). Similar problem where the QP will inexplicably decide one day to make a query really slow and you gotta override it.
Re: Postgres is eating the database world
#10Postgres is simply the best. One thing I would like however is the ability to have control over the query planner for specific tasks. There is a dark art to influencing the query planner, but essentially it is unpredictable, and postgres can get it consistently wrong in certain scenarios. If you could just enable a special query mode that gives you absolute control over the QP for that query, it would solve a major p…
MySQL offers this via use/force index (…). Similar problem where the QP will inexplicably decide one day to make a query really slow and you gotta override it.
We have a couple queries where using the correct index they'll take milliseconds, using the wrong index it'll take minutes - and mysql occasionally enough to be a noticeable load on the database chooses the wrong one and we've specified "USE INDEX" even though I really hate having to do so.