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Prior to this patch, every FETCH call would generate a unique queryId with a different size specified. Depending on the workloads, this could lead to a significant bloat in pg_stat_statements, as repeatedly calling a specific cursor would result in a new queryId each time. For example, FETCH 1 c1; and FETCH 2 c1; would produce different queryIds. This patch improves the situation by normalizing the fetch size, so as semantically similar statements generate the same queryId. As a result, statements like the below, which differ syntactically but have the same effect, will now share a single queryId: FETCH FROM c1 FETCH NEXT c1 FETCH 1 c1 In order to do a normalization based on the keyword used in FETCH, FetchStmt is tweaked with a new FetchDirectionKeywords. This matters for "howMany", which could be set to a negative value depending on the direction, and we want to normalize the queries with enough information about the direction keywords provided, including RELATIVE, ABSOLUTE or all the ALL variants. Author: Sami Imseih <samimseih@gmail.com> Discussion: https://postgr.es/m/CAA5RZ0tA6LbHCg2qSS+KuM850BZC_+ZgHV7Ug6BXw22TNyF+MA@mail.gmail.com
208 lines
4.0 KiB
Plaintext
208 lines
4.0 KiB
Plaintext
--
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-- Cursors
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--
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-- These tests require track_utility to be enabled.
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SET pg_stat_statements.track_utility = TRUE;
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SELECT pg_stat_statements_reset() IS NOT NULL AS t;
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t
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---
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t
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(1 row)
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-- DECLARE
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-- SELECT is normalized.
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DECLARE cursor_stats_1 CURSOR WITH HOLD FOR SELECT 1;
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CLOSE cursor_stats_1;
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DECLARE cursor_stats_1 CURSOR WITH HOLD FOR SELECT 2;
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CLOSE cursor_stats_1;
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SELECT calls, rows, query FROM pg_stat_statements ORDER BY query COLLATE "C";
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calls | rows | query
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-------+------+-------------------------------------------------------
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2 | 0 | CLOSE cursor_stats_1
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2 | 0 | DECLARE cursor_stats_1 CURSOR WITH HOLD FOR SELECT $1
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1 | 1 | SELECT pg_stat_statements_reset() IS NOT NULL AS t
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(3 rows)
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SELECT pg_stat_statements_reset() IS NOT NULL AS t;
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t
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---
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t
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(1 row)
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-- FETCH
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BEGIN;
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DECLARE cursor_stats_1 CURSOR WITH HOLD FOR SELECT 2;
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DECLARE cursor_stats_2 CURSOR WITH HOLD FOR SELECT 3;
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FETCH 1 IN cursor_stats_1;
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?column?
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----------
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2
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(1 row)
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FETCH 1 IN cursor_stats_2;
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?column?
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----------
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3
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(1 row)
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CLOSE cursor_stats_1;
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CLOSE cursor_stats_2;
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COMMIT;
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SELECT calls, rows, query FROM pg_stat_statements ORDER BY query COLLATE "C";
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calls | rows | query
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-------+------+-------------------------------------------------------
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1 | 0 | BEGIN
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1 | 0 | CLOSE cursor_stats_1
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1 | 0 | CLOSE cursor_stats_2
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1 | 0 | COMMIT
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1 | 0 | DECLARE cursor_stats_1 CURSOR WITH HOLD FOR SELECT $1
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1 | 0 | DECLARE cursor_stats_2 CURSOR WITH HOLD FOR SELECT $1
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1 | 1 | FETCH $1 IN cursor_stats_1
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1 | 1 | FETCH $1 IN cursor_stats_2
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1 | 1 | SELECT pg_stat_statements_reset() IS NOT NULL AS t
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(9 rows)
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SELECT pg_stat_statements_reset() IS NOT NULL AS t;
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t
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---
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t
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(1 row)
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-- Normalization of FETCH statements
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BEGIN;
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DECLARE pgss_cursor CURSOR FOR SELECT FROM generate_series(1, 10);
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-- implicit directions
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FETCH pgss_cursor;
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--
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(1 row)
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FETCH 1 pgss_cursor;
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--
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(1 row)
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FETCH 2 pgss_cursor;
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--
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(2 rows)
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FETCH -1 pgss_cursor;
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--
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(1 row)
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-- explicit NEXT
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FETCH NEXT pgss_cursor;
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--
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(1 row)
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-- explicit PRIOR
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FETCH PRIOR pgss_cursor;
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--
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(1 row)
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-- explicit FIRST
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FETCH FIRST pgss_cursor;
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--
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(1 row)
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-- explicit LAST
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FETCH LAST pgss_cursor;
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--
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(1 row)
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-- explicit ABSOLUTE
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FETCH ABSOLUTE 1 pgss_cursor;
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--
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(1 row)
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FETCH ABSOLUTE 2 pgss_cursor;
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--
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(1 row)
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FETCH ABSOLUTE -1 pgss_cursor;
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--
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(1 row)
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-- explicit RELATIVE
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FETCH RELATIVE 1 pgss_cursor;
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--
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(0 rows)
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FETCH RELATIVE 2 pgss_cursor;
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--
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(0 rows)
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FETCH RELATIVE -1 pgss_cursor;
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--
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(1 row)
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-- explicit FORWARD
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FETCH ALL pgss_cursor;
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--
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(0 rows)
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-- explicit FORWARD ALL
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FETCH FORWARD ALL pgss_cursor;
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--
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(0 rows)
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-- explicit FETCH FORWARD
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FETCH FORWARD pgss_cursor;
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--
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(0 rows)
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FETCH FORWARD 1 pgss_cursor;
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--
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(0 rows)
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FETCH FORWARD 2 pgss_cursor;
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--
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(0 rows)
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FETCH FORWARD -1 pgss_cursor;
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--
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(1 row)
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-- explicit FETCH BACKWARD
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FETCH BACKWARD pgss_cursor;
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--
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(1 row)
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FETCH BACKWARD 1 pgss_cursor;
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--
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(1 row)
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FETCH BACKWARD 2 pgss_cursor;
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--
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(2 rows)
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FETCH BACKWARD -1 pgss_cursor;
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--
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(1 row)
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-- explicit BACKWARD ALL
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FETCH BACKWARD ALL pgss_cursor;
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--
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(6 rows)
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COMMIT;
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SELECT calls, query FROM pg_stat_statements ORDER BY query COLLATE "C";
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calls | query
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-------+--------------------------------------------------------------------
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1 | BEGIN
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1 | COMMIT
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1 | DECLARE pgss_cursor CURSOR FOR SELECT FROM generate_series($1, $2)
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3 | FETCH ABSOLUTE $1 pgss_cursor
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1 | FETCH ALL pgss_cursor
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1 | FETCH BACKWARD ALL pgss_cursor
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4 | FETCH BACKWARD pgss_cursor
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1 | FETCH FIRST pgss_cursor
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1 | FETCH FORWARD ALL pgss_cursor
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4 | FETCH FORWARD pgss_cursor
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1 | FETCH LAST pgss_cursor
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1 | FETCH NEXT pgss_cursor
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1 | FETCH PRIOR pgss_cursor
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3 | FETCH RELATIVE $1 pgss_cursor
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4 | FETCH pgss_cursor
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1 | SELECT pg_stat_statements_reset() IS NOT NULL AS t
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(16 rows)
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