Re: queryId constant squashing does not support prepared statements

> The test additions done in v7-0002 look sensible here.
>
> --- In the following two queries the operator expressions (+) and (@) have
> --- different oppno, and will be given different query_id if squashed, even though
> --- the normalized query will be the same
>
> In v7-0002, this comment is removed, but it still applies, isn't it?

No, the comment is wrong/misleading even in HEAD. The output looks
like the below so, the normalized query will not be the same and the
queries will also not be squashed.

```
SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
                                               query
                             | calls
----------------------------------------------------------------------------------------------------+-------
 SELECT * FROM test_squash WHERE id IN
                            +|     2
         ($1 + $2, $3 + $4, $5 + $6, $7 + $8, $9 + $10, $11 + $12, $13
+ $14, $15 + $16, $17 + $18) |
 SELECT * FROM test_squash WHERE id IN
                            +|     2
         (@ $1, @ $2, @ $3, @ $4, @ $5, @ $6, @ $7, @ $8, @ $9)
                             |
 SELECT pg_stat_statements_reset() IS NOT NULL AS t
                             |     1
(3 rows)
```

so I felt a much simpler and more appropriate comment is

```
-- No constants squashing for OpExpr
```


> --- Bigint, explicit cast is not squashed
> +-- Bigint, explicit cast is squashed
>
> Seems incorrect with 0002 taken in isolation.  The last cast is still
> present in the normalization.  It's not after v7-0003.

in 0002, this is still a squashed string even if the "::bigint" still appears at
the end of the string. Squashing is replacing the elements with
 "$1 /*, ... */"
```
----------------------------------------------------+-------
 SELECT * FROM test_squash_bigint WHERE data IN    +|     2
         ($1 /*, ... */::bigint)
```
0003 improves/fixes this by truly squashing between the entire
boundary of the list.

> Already mentioned upthread, but applying only v7-0003 on top of
> v7-0002 (not v7-0004) leads to various regression failures in dml.sql
> and squashing.sql.  The failures persist with v7-0004 applied.  Please
> see these as per the attached, the IN lists do not get squashed, the
> array elements are.  Just to make sure that I am not missing
> something, I've rebuilt from scratch with no success.

I cannot reproduce this. I applied each patch (v7-0002, 0003)
in order and ran "make check" on pg_stat_statements for every apply,
and I could not reproduce. Not sure what you and I are doing different?

I also could not reproduce with the v8 patch series either.

> IsSquashableExpressionList() includes this comment, which is outdated,
> probably because squashing was originally optional behind a GUC and
> the parameter has been removed while the comment has not been
> refreshed:
>     /*
>      * If squashing is disabled, or the list is too short, we don't try to
>      * squash it.
>      */

Thanks for reminding me about this. I remember seeing it, but missed
fixing it. Corrected now.

> RecordExpressionLocation()'s top comment needs a refresh, talking
> about constants.  The simplifications gained in pgss.c's normalization
> are pretty cool.

Yes, missed this also. Done.

> +   bool        has_squashed_lists;
> [...]
> +   if (jstate->has_squashed_lists)
> +       jstate->highest_extern_param_id = 0;
>
> This new flag in JumbleState needs to be documented, explaining why
> it needs to be here.

Done. I felt that combining highest_extern_param_id and
has_squashed_lists in the
same comment made the most sense, as they are closely related.

-    /* highest Param id we've seen, in order to start normalization
correctly */
+    /*
+     * Highest Param id we've seen, in order to start normalization correctly.
+     * However, if the jumble contains at least one squashed list, we
+     * disregard the highest_extern_param_id value because parameters can
+     * exist within the squashed list and are no longer considered for
+     * normalization.
+     */
     int            highest_extern_param_id;
+    bool        has_squashed_lists;


> I have to admit that it is strange to see
> highest_extern_param_id, one value in JumbleState be forced to zero in
> the PGSS normalization code if has_squashed_lists is set to true.
> This seems like a layer violation to me

Yeah, that's silly of me. This should be done in DoJumble after
_jumbleNode. Fixed.

I also reorganized the tests in extended.out to make them more readable,
namely I wanted to show separate outputs for what is tested
for "-- Unique query IDs with parameter numbers switched." and what is tested
for "-- Two groups of two queries with the same query ID."

I also added a comment for
``
bool extern_param;
```

v8 addresses the above.


--
Sami Imseih
Amazon Web Services (AWS)