Re: [HACKERS] New SQL counter statistics view (pg_stat_sql) - Mailing list pgsql-hackers

On Sat, Jan 14, 2017 at 2:58 AM, Dilip Kumar <dilipbalaut@gmail.com> wrote:

On Wed, Jan 11, 2017 at 7:47 PM, Dilip Kumar <dilipbalaut@gmail.com> wrote:
> +void
> +pgstat_count_sqlstmt(const char *commandTag)
> +{
> + PgStat_SqlstmtEntry *htabent;
> + bool found;
> +
> + if (!pgstat_track_sql)
> + return
>
> Callers of pgstat_count_sqlstmt are always ensuring that
> pgstat_track_sql is true, seems it's redundant here.

I have done testing of the feature, it's mostly working as per the expectation.

Thanks for the review and test.

The use case for this view is to find out the number of different SQL statements

that are getting executed successfully on an instance by the application/user. 

I have few comments/questions.

--------
If you execute the query with EXECUTE then commandTag will be EXECUTE
that way we will not show the actual query type, I mean all the
statements will get the common tag "EXECUTE".

You can try this.
PREPARE fooplan (int) AS INSERT INTO t VALUES($1);
EXECUTE fooplan(1);

------

Yes, that's correct. Currently the count is incremented based on the base command,

because of this reason, the EXECUTE is increased, instead of the actual operation.

 

+ /* Destroy the SQL statement counter stats HashTable */
+ hash_destroy(pgstat_sql);
+
+ /* Create SQL statement counter Stats HashTable */

I think in the patch we have used mixed of "Stats HashTable" and
"stats HashTable", I think better
to be consistent throughout the patch. Check other similar instances.

----------------

Corrected.

 

@@ -1102,6 +1102,12 @@ exec_simple_query(const char *query_string)

  PortalDrop(portal, false);

+ /*
+ * Count SQL statement for pg_stat_sql view
+ */
+ if (pgstat_track_sql)
+ pgstat_count_sqlstmt(commandTag);

We are only counting the successful SQL statement, Is that intentional?

Yes, I thought of counting the successful SQL operations that changed the

database over a period of time. I am not sure whether there will be many

failure operations that can occur on an instance to be counted.

 

------
I have noticed that pgstat_count_sqlstmt is called from
exec_simple_query and exec_execute_message. Don't we want to track the
statement executed from functions?
-------

 

The view is currently designed to count user/application initiated SQL statements,

but not the internal SQL queries that are getting executed from functions and etc.

>>+void
>>+pgstat_count_sqlstmt(const char *commandTag)
>>+{
>>+ PgStat_SqlstmtEntry *htabent;
>>+ bool found;
>>+
>>+ if (!pgstat_track_sql)
>>+ return
>
>Callers of pgstat_count_sqlstmt are always ensuring that
>pgstat_track_sql is true, seems it's redundant here.

Removed the check in pgstat_count_sqlstmt statement and add it exec_execute_message

function where the check is missed.

Updated patch attached.

I have reviewed the patch. All the test cases works fine.

Regards,
Vinayak Pokale
NTT Open Source Software Center