Looking Forward to Postgres 19: Query Hints

Its also worth reading the original post by Robert Haas (the author of pg_plan_advice) on motivation/design: https://rhaas.blogspot.com/2026/03/pgplanadvice-plan-stabili...

Also, I'll add my perspective: I think "EXPLAIN (PLAN_ADVICE)" is a key piece to making this a plan stability feature, not (just) a hinting feature. The extensibility/framework pg_plan_advice adds is a foundation, that over time will over time address the age-old "Postgres doesn't have hints" problem, even if the initial release doesn't check all the boxes yet, e.g. no way to use advice for adjusting row/join estimates.

To give an example on extensibility: Some people that I've spoken to are asking "but why is it not a comment-style hint". There are reasons why Postgres didn't go that way for this release (comment parsing in core is non-existent today, and comments don't work correctly e.g. for functions), but its easy to write an extension that sets up an advisor hook to parse comments: https://github.com/pganalyze/pg_advice_comment

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trollbridge 3 hours ago | parent | prev | next [-]

Shudder. Flashbacks to having to write optimiser hints in Oracle (and the resulting fun times when you'd upgrade the database, something would change, and your hints would make a query slower).

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winrid an hour ago | parent | next [-]

As opposed to not upgrading and the planner picking a plan at 3am that is slower?

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jeffbee 2 hours ago | parent | prev [-]

I can't believe we're still doing this. You should be able to dictate the query execution without involving a planner.

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timacles 2 hours ago | parent [-]

I really don’t think you’re considering all the edge cases in such a scenario.

Most devs have problems writing decent queries (in some situations), now you want to introduce writing the query execution plan into the mix ?

	▲	akoboldfrying an hour ago \| parent [-]
		No one is taking away the existing automatic planning that works well 95% of the time. You're welcome to continue using that. The worst thing that could possibly happen is that you give it bad advice leading to slow queries, and then the obvious first step to fixing that is to drop the manual advice and see whether the automatic planner handles it better. It baffles me that PostgreSQL, which is so deeply customisable in almost every other way, resisted this form of customisability for so long. This is great news.

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crimsonnoodle58 6 hours ago | parent | prev | next [-]

> How many of us have toggled enable_seqscan to off to force an index scan? Or thrown an OFFSET 0 into a subquery to prevent the planner from flattening it?

enable_nestloop = off here.

For us, joining many complex views quickly trips the planner up, so I'm really glad to see this.

> They break on upgrades.

The irony is so does the planner. I've seen queries working perfectly fine in older PG's suddenly run away in newer versions. So hints will actually bring stability.

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da_chicken 3 hours ago | parent | next [-]

The planner breaking on updates is common for almost all RDBMSs. They introduce optimizations that work great for 95% of customers, and some will just have queries that now act like cardinality is way off or covering indexes are missing.

	▲	mpyne 2 hours ago \| parent [-]
		This issue was one of AWS's listed reasons for tending to prefer NoSQL style databases over "more performant" RDBMS, because of the more consistent worst-case performance, even if the result is worse average-case performance, which was important in their assumptions for scalability planning.

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throwatdem12311 2 hours ago | parent | prev [-]

Every single time I’ve thought I’ve needed to try these it made it worse.

Every time Claude tries to tell me to try these, it made it worse.

Not once has it made it better for me. I’m doing materialized view refreshes with a billion rows, which is small enough maybe that this doesn’t come into play…but so far the planner knows best.

If the database can’t make it fast with just smart joins and filtering then it’s the architecture that’s a problem, not the database.

Usually the only thing I need to do is increase work_mem.

	▲	silon42 an hour ago \| parent [-]
		The hints are needed when you have a web scale / online transaction processing application, where you want to guarantee no table scan ever. Ideally, I'd want to rrun without statistics on the tables in that case (ie, no smart joins).

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cryptonector an hour ago | parent | prev | next [-]

> The advice language is surprisingly expressive for something the community resisted for decades.

FINALLY!

I like this design.

And yes, the community resisted this for way too long.

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robertlagrant 6 hours ago | parent | prev | next [-]

I'm not an expert in database hints, but the syntax looks very readable and composable. That's great thing to have got right.

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aeontech 2 hours ago | parent | prev | next [-]

Very interesting - I just installed pg_hint_plan [0] extension a few months ago to get around a query that was confusing the planner too much. Edge case, but when you need it you really need it.

Haven't seen pg_plan_advice before, TIL!

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jbellis 5 hours ago | parent | prev [-]

man, Tom Lane has hated query hints for literally decades

did he finally come around?

	▲	lfittl 5 hours ago \| parent [-]
		I don't think Tom's perspective has necessarily changed (and there is certainly concern from others that this could cause less reports on planner bugs), but Tom is pretty good about not standing in the way of others (i.e. Robert Haas in this case) trying to make things work, and being open to new perspectives. I do know that one of the important criteria for getting this in was that a bad advice can't cause the planner to fail, and that's something that was explicitly included in the design of pg_plan_advice.