Re: [PATCH] Increase the maximum value track_activity_query_size

Nikolay Samokhvalov <samokhvalov(at)gmail(dot)com> writes:
> Here is what ORMs do:
> select length('SELECT "column_name_1001", "column_name_1002",
> "column_name_1003", "column_name_1004", "column_name_1005",
> "column_name_1006", "column_name_1007", "column_name_1008",
> "column_name_1009", "column_name_1010", "column_name_1011",
> "column_name_1012", "column_name_1013", "column_name_1014",
> "column_name_1015", "column_name_1016", "column_name_1017",
> "column_name_1018", "column_name_1019", "column_name_1020",
> "column_name_1021", "column_name_1022", "column_name_1023",
> "column_name_1024", "column_name_1025", "column_name_1026",
> "column_name_1027", "column_name_1028", "column_name_1029",
> "column_name_1030", "column_name_1031", "column_name_1032",
> "column_name_1033", "column_name_1034", "column_name_1035",
> "column_name_1036", "column_name_1037", "column_name_1038",
> "column_name_1039", "column_name_1040", "column_name_1041",
> "column_name_1042", "column_name_1043", "column_name_1044",
> "column_name_1045", "column_name_1046", "column_name_1047",
> "column_name_1048", "column_name_1049", "column_name_1050" FROM
> "some_table";');
> length
> --------
> 1024
> (1 row)

> That's it – with default settings, you won't see WHERE clause or
> anything else.

If that's true, it doesn't offer much of a case for upping the limit
on track_activity_query_size. The longest such a query could reasonably
get is somewhere near NAMEDATALEN times MaxHeapAttributeNumber, which
as it happens is exactly the existing limit on track_activity_query_size.

> As a result, many queries exceed track_activity_query_size

How? And if they are, why do you care? Such queries sure seem
pretty content-free.

> What is the overhead here except the memory consumption?

The time to copy those strings out of shared storage, any time
you query pg_stat_activity.

regards, tom lane