Re: [PATCH] Use $ parameters as replacement characters for pg_stat_statements

On Sat, Mar 4, 2017 at 1:52 PM, Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
> On Sat, Mar 4, 2017 at 8:02 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>> Perhaps there could be a choice of behaviors. Even if we all agreed
>>> that parameter notation was better in theory, there's something to be
>>> said for maintaining backward compatibility, or having an option to do
>>> so.
>>
>> Meh ... we've generally regretted it when we "solved" a backwards
>> compatibility problem by introducing a GUC that changes query semantics.
>> I'm inclined to think we should either do it or not.
>
> In my opinion, we expose query id (and dbid, and userid) as the
> canonical identifier for each pg_stat_statements entry, and have done
> so for some time. That's the stable API -- not query text. I'm aware
> of cases where query text was used as an identifier, but that ended up
> being hashed anyway.
>
> Query text is just for human consumption.

Lukas evidently thinks otherwise, based on the original post.

> I'd be in favor of a change
> that makes it easier to copy and paste a query, to run EXPLAIN and so
> on. Lukas probably realizes that there are no guarantees that the
> query text that appears in pg_stat_statements will even appear as
> normalized in all cases. The "sticky entry" stuff is intended to
> maximize the chances of that happening, but it's still generally quite
> possible (e.g. pg_stat_statements never swaps constants in a query
> like "SELECT 5, pg_stat_statements_reset()"). This means that we
> cannot really say that this buys us a machine-readable query text
> format, at least not without adding some fairly messy caveats.

Well, Lukas's original suggestion of using $n for a placeholder would
do that, unless there's already a $n with the same numerical value,
but Andres's proposal to use $-n or $:n would not.

--
Robert Haas
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