Thread

Re: Why isn't PG using an index-only scan?

Andrei Lepikhov <lepihov@gmail.com> — 2025-09-18T11:55:02Z

On 18/9/2025 13:35, David Rowley wrote:
> On Thu, 18 Sept 2025 at 19:55, Andrei Lepikhov <lepihov@gmail.com> wrote:
>> Imagine if we had a hook within the ExecProcNode. In that scenario, we
>> could create a trivial extension that would stop the query after, let's
>> say, 10 minutes of execution and display the current state. This would
>> give us more reliable data on estimation and the state of the plan tree.
> 
> I recall something along those lines existing once in the extension
> world. Or maybe just from a previous employer. I don't recall many of
> the details. Maybe something like a function you pass an SQL string
> and if you cancelled the query it reported the EXPLAIN ANALYZE done so
> far. I assume it must have done something like LOG it as it couldn't
> have shown the EXPLAIN as query results on cancel.
It looks like a makeshift solution. By implementing a callback, we could 
elevate 'interrupter' to a first-class feature, enabling us to monitor 
the state of the entire query tree (it is especially cool in EXPLAIN 
ANALYZE mode when we may be OK with a partial result).
What's more interesting if Robert's work on nodes' extensibility 
successes, it enables modules to save planning decisions in the plan. 
Thereby, the in-executor callback provides a means to kick off the query 
planned with incorrect estimations (e.g., too many spilled tuples).

Perhaps we should start working on introducing this type of callback/ hook?

-- 
regards, Andrei Lepikhov