* Denormalize prepared statement queries
Added support for extracting query arguments for prepared statements
when `pg_stat_monitor.pgsm_normalized_query` is off.
Previously pg_stat_monitor was unable to extract the arguments for
prepared statements, thus leaving queries with placeholders $1
.. $N instead of the actual arguments.
* Optmize query denormalization
Instead of copying original query text byte by byte, copy data between
query placeholders in chunks, example:
`INSERT INTO foo(a, b, c) VALUES('test', 100, 'test again)'`
Would result in normalized query:
`INSERT INTO foo(a, b, c) VALUES($1, $2, $3)`
The original patch would copy the parts between placeholders byte by
byte, e.g. `INSERT INTO foo(a, b, c) VALUES(`, instead we can copy this
whole block at once, 1 function call and maybe 1 buffer re-allocation
per call.
Also make use of `appendBinaryStringInfo` to avoid calculating string
length as we have this info already.
* Optmize query denormalization(2)
Avoid allocating an array of strings for extracting query argument
values, instead append the current parameter value directly in the
buffer used to store the denormalized query.
This avoids not only unnecessary memory allocations, but also copying
data between temporary memory and the buffer.
* Store denormalized query only under certain constraints
This commit introduces a little optimization along with a feature, it
stores the query in denormalized form only under the circumstances
below:
- The psgm_normalized_query GUC is disabled (off).
- The query is seem for the first time, or the query total
execution time exceeds the mean execution time calculated for
the previous queries.
Having the query which took most execution time along with it's
arguments could help users in further investigating performance issues.
* Fix regression tests
When query normalization is disabled utility queries like SELECT 10+20
are now stored as is, instead of SELECT $1+$2.
Also when functions or sub queries are created the arguments used
internally by the function or subqueries will be replaced by NULL instead
of $1..$N. The actual arguments will be displayed when the function or
subquery is actually invoked.
* Add query denormalization regression test for prepared statements
Ensures that the denormalization of prepared statements is working, also
ensure that a query which takes more time to execute replaces the
previous denormalized query.
* Updated pgsm_query_id regression tests
With the query dernomalization feature, having integer literals used in
sql like 1, or 2 could create some confusion on whether those are
placeholders or constant values, thus this commit updates the
pgsm_query_id regression test to use different integer literals to avoid
confusion.
* Improve query denormalization regression test
Add a new test case:
1. Execute a prepared statement with larger execution time first.
2. Execute the same prepared statement with cheap execution time.
3. Ensures that the denormalized heavy query is not replaced by the
cheaper.
* Format source using pgindent
* Fix top query regression tests on PG 12,13
On PG 12, 13, the internal return instruction in the following function:
```
CREATE OR REPLACE FUNCTION add(int, int) RETURNS INTEGER AS
$$
BEGIN
return (select $1 + $2);
END; $$ language plpgsql;
```
Is stored as SELECT (select expr1 + expr2)
On PG 14 onward it's stored just as SELECT (expr1 + expr2)
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