diff options
Diffstat (limited to 'doc/src/sgml/pgstatstatements.sgml')
| -rw-r--r-- | doc/src/sgml/pgstatstatements.sgml | 29 |
1 files changed, 21 insertions, 8 deletions
diff --git a/doc/src/sgml/pgstatstatements.sgml b/doc/src/sgml/pgstatstatements.sgml index d4f09fc2a3a..082994cae00 100644 --- a/doc/src/sgml/pgstatstatements.sgml +++ b/doc/src/sgml/pgstatstatements.sgml @@ -244,11 +244,12 @@ </para> <para> - When a constant's value has been ignored for purposes of matching the - query to other queries, the constant is replaced by <literal>?</literal> - in the <structname>pg_stat_statements</> display. The rest of the query - text is that of the first query that had the particular - <structfield>queryid</> hash value associated with the + When a constant's value has been ignored for purposes of matching the query + to other queries, the constant is replaced by a parameter symbol, such + as <literal>$1</literal>, in the <structname>pg_stat_statements</> + display. + The rest of the query text is that of the first query that had the + particular <structfield>queryid</> hash value associated with the <structname>pg_stat_statements</> entry. </para> @@ -302,6 +303,18 @@ </para> <para> + The parameter symbols used to replace constants in + representative query texts start from the next number after the + highest <literal>$</><replaceable>n</> parameter in the original query + text, or <literal>$1</> if there was none. It's worth noting that in + some cases there may be hidden parameter symbols that affect this + numbering. For example, <application>PL/pgSQL</> uses hidden parameter + symbols to insert values of function local variables into queries, so that + a <application>PL/pgSQL</> statement like <literal>SELECT i + 1 INTO j</> + would have representative text like <literal>SELECT i + $2</>. + </para> + + <para> The representative query texts are kept in an external disk file, and do not consume shared memory. Therefore, even very lengthy query texts can be stored successfully. However, if many long query texts are @@ -481,13 +494,13 @@ bench=# SELECT query, calls, total_time, rows, 100.0 * shared_blks_hit / nullif(shared_blks_hit + shared_blks_read, 0) AS hit_percent FROM pg_stat_statements ORDER BY total_time DESC LIMIT 5; -[ RECORD 1 ]--------------------------------------------------------------------- -query | UPDATE pgbench_branches SET bbalance = bbalance + ? WHERE bid = ?; +query | UPDATE pgbench_branches SET bbalance = bbalance + $1 WHERE bid = $2; calls | 3000 total_time | 9609.00100000002 rows | 2836 hit_percent | 99.9778970000200936 -[ RECORD 2 ]--------------------------------------------------------------------- -query | UPDATE pgbench_tellers SET tbalance = tbalance + ? WHERE tid = ?; +query | UPDATE pgbench_tellers SET tbalance = tbalance + $1 WHERE tid = $2; calls | 3000 total_time | 8015.156 rows | 2990 @@ -499,7 +512,7 @@ total_time | 310.624 rows | 100000 hit_percent | 0.30395136778115501520 -[ RECORD 4 ]--------------------------------------------------------------------- -query | UPDATE pgbench_accounts SET abalance = abalance + ? WHERE aid = ?; +query | UPDATE pgbench_accounts SET abalance = abalance + $1 WHERE aid = $2; calls | 3000 total_time | 271.741999999997 rows | 3000 |