| From: | "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> |
|---|---|
| To: | Richard Michael <rmichael(at)edgeofthenet(dot)org> |
| Cc: | "pgsql-general(at)postgresql(dot)org" <pgsql-general(at)postgresql(dot)org> |
| Subject: | Re: How to observe plan_cache_mode transition from custom to generic plan? |
| Date: | 2021-09-05 18:32:41 |
| Message-ID: | CAKFQuwYvmmhDjX+StTV8oDVMcPPQ0eTJ-pJep0VSB2RZyy+oNw@mail.gmail.com |
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| Lists: | pgsql-general |
On Sunday, September 5, 2021, Richard Michael <rmichael(at)edgeofthenet(dot)org>
wrote:
>
> Based on the documentation, I expected the first planned query text to
> be: `SELECT 10 AS data`, since it should be a custom plan with
> substituted values. However, the query text always contains a parameter
> symbol: `SELECT $1 AS data`.
>
>
A query plan is not the same as the query text. While the executed plan
can be generic or custom the query text is constant.
If you want to see the difference between a generic and a custom plan you
need to comprise a query that would actually have different custom and
generic plans. Queries that don’t involve tables, indexes, or joins don’t
have any choices to make with respect to how they are executed.
David J.
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