This is a proposal for a new feature in pg_stat_statements extension.
As a statistical extension providing counters pg_stat_statements
extension is a target for various sampling solutions. All of them
interested in calculation of statement statistics increments between
two samples. But we face a problem here - observing one statement with
its statistics right now we can't be sure that statistics increment for
this statement is continuous from previous sample. This statement could
be deallocated after previous sample and come back soon. Also it could
happen that statement executions after that increased statistics to
above the values we observed in previous sample making it impossible to
detect deallocation on statement level.
My proposition here is to store statement entry timestamp. In this case
any sampling solution in case of returning statement will easily detect
it by changed timestamp value. And for every statement we will know
exact time interval for its statistics.
diff --git a/contrib/pg_stat_statements/expected/pg_stat_statements.out b/contrib/pg_stat_statements/expected/pg_stat_statements.out
index 16158525ca..ffe08dece5 100644
--- a/contrib/pg_stat_statements/expected/pg_stat_statements.out
+++ b/contrib/pg_stat_statements/expected/pg_stat_statements.out
@@ -876,4 +876,26 @@ SELECT dealloc FROM pg_stat_statements_info;
0
(1 row)
+--
+-- statement timestamps
+--
+SELECT pg_stat_statements_reset();
+ pg_stat_statements_reset
+--------------------------
+
+(1 row)
+
+SELECT now() AS start_ts \gset
+SELECT 1 AS "STMTTS";
+ STMTTS
+--------
+ 1
+(1 row)
+
+SELECT count(*) FROM pg_stat_statements WHERE first_seen >= :'start_ts' AND query LIKE '%STMTTS%';
+ count
+-------
+ 1
+(1 row)
+
DROP EXTENSION pg_stat_statements;
diff --git a/contrib/pg_stat_statements/pg_stat_statements--1.8--1.9.sql b/contrib/pg_stat_statements/pg_stat_statements--1.8--1.9.sql
index 3504ca7eb1..9842d2da49 100644
--- a/contrib/pg_stat_statements/pg_stat_statements--1.8--1.9.sql
+++ b/contrib/pg_stat_statements/pg_stat_statements--1.8--1.9.sql
@@ -3,6 +3,60 @@
-- complain if script is sourced in psql, rather than via ALTER EXTENSION
\echo Use "ALTER EXTENSION pg_stat_statements UPDATE TO '1.9'" to load this file. \quit
+/* We need to redefine a view and a function */
+/* First we have to remove them from the extension */
+ALTER EXTENSION pg_stat_statements DROP VIEW pg_stat_statements;
+ALTER EXTENSION pg_stat_statements DROP FUNCTION pg_stat_statements(boolean);
+
+/* Then we can drop them */
+DROP VIEW pg_stat_statements;
+DROP FUNCTION pg_stat_statements(boolean);
+
+/* Now redefine */
+CREATE FUNCTION pg_stat_statements(IN showtext boolean,
+ OUT userid oid,
+ OUT dbid oid,
+ OUT queryid bigint,
+ OUT query text,
+ OUT plans int8,
+ OUT total_plan_time float8,
+ OUT min_plan_time float8,
+ OUT max_plan_time float8,
+ OUT mean_plan_time float8,
+ OUT stddev_plan_time float8,
+ OUT calls int8,
+ OUT total_exec_time float8,
+ OUT min_exec_time float8,
+ OUT max_exec_time float8,
+ OUT mean_exec_time float8,
+ OUT stddev_exec_time float8,
+ OUT rows int8,
+ OUT shared_blks_hit int8,
+ OUT shared_blks_read int8,
+ OUT shared_blks_dirtied int8,
+ OUT shared_blks_written int8,
+ OUT local_blks_hit int8,
+ OUT local_blks_read int8,
+ OUT local_blks_dirtied int8,
+ OUT local_blks_written int8,
+ OUT temp_blks_read int8,
+ OUT temp_blks_written int8,
+ OUT blk_read_time float8,
+ OUT blk_write_time float8,
+ OUT wal_records int8,
+ OUT wal_fpi int8,
+ OUT wal_bytes numeric,
+ OUT first_seen timestamp with time zone
+)
+RETURNS SETOF record
+AS 'MODULE_PATHNAME', 'pg_stat_statements_1_9'
+LANGUAGE C STRICT VOLATILE PARALLEL SAFE;
+
+CREATE VIEW pg_stat_statements AS
+ SELECT * FROM pg_stat_statements(true);
+
+GRANT SELECT ON pg_stat_statements TO PUBLIC;
+
--- Define pg_stat_statements_info
CREATE FUNCTION pg_stat_statements_info(
OUT dealloc bigint,
diff --git a/contrib/pg_stat_statements/pg_stat_statements.c b/contrib/pg_stat_statements/pg_stat_statements.c
index 62cccbfa44..70b08d36c8 100644
--- a/contrib/pg_stat_statements/pg_stat_statements.c
+++ b/contrib/pg_stat_statements/pg_stat_statements.c
@@ -99,7 +99,7 @@ PG_MODULE_MAGIC;
#define PGSS_TEXT_FILE PG_STAT_TMP_DIR "/pgss_query_texts.stat"
/* Magic number identifying the stats file format */
-static const uint32 PGSS_FILE_HEADER = 0x20201218;
+static const uint32 PGSS_FILE_HEADER = 0x20210322;
/* PostgreSQL major version number, changes in which invalidate all entries */
static const uint32 PGSS_PG_MAJOR_VERSION = PG_VERSION_NUM / 100;
@@ -125,7 +125,8 @@ typedef enum pgssVersion
PGSS_V1_1,
PGSS_V1_2,
PGSS_V1_3,
- PGSS_V1_8
+ PGSS_V1_8,
+ PGSS_V1_9
} pgssVersion;
typedef enum pgssStoreKind
@@ -217,6 +218,7 @@ typedef struct pgssEntry
Size query_offset; /* query text offset in external file */
int query_len; /* # of valid bytes in query string, or -1 */
int encoding; /* query text encoding */
+ TimestampTz first_seen; /* timestamp of entry allocation moment */
slock_t mutex; /* protects the counters only */
} pgssEntry;
@@ -337,6 +339,7 @@ PG_FUNCTION_INFO_V1(pg_stat_statements_reset_1_7);
PG_FUNCTION_INFO_V1(pg_stat_statements_1_2);
PG_FUNCTION_INFO_V1(pg_stat_statements_1_3);
PG_FUNCTION_INFO_V1(pg_stat_statements_1_8);
+PG_FUNCTION_INFO_V1(pg_stat_statements_1_9);
PG_FUNCTION_INFO_V1(pg_stat_statements);
PG_FUNCTION_INFO_V1(pg_stat_statements_info);
@@ -684,6 +687,7 @@ pgss_shmem_startup(void)
/* copy in the actual stats */
entry->counters = temp.counters;
+ entry->first_seen = temp.first_seen;
}
/* Read global statistics for pg_stat_statements */
@@ -1511,7 +1515,8 @@ pg_stat_statements_reset(PG_FUNCTION_ARGS)
#define PG_STAT_STATEMENTS_COLS_V1_2 19
#define PG_STAT_STATEMENTS_COLS_V1_3 23
#define PG_STAT_STATEMENTS_COLS_V1_8 32
-#define PG_STAT_STATEMENTS_COLS 32 /* maximum of above */
+#define PG_STAT_STATEMENTS_COLS_V1_9 33
+#define PG_STAT_STATEMENTS_COLS 33 /* maximum of above */
/*
* Retrieve statement statistics.
@@ -1523,6 +1528,16 @@ pg_stat_statements_reset(PG_FUNCTION_ARGS)
* expected API version is identified by embedding it in the C name of the
* function. Unfortunately we weren't bright enough to do that for 1.1.
*/
+Datum
+pg_stat_statements_1_9(PG_FUNCTION_ARGS)
+{
+ bool showtext = PG_GETARG_BOOL(0);
+
+ pg_stat_statements_internal(fcinfo, PGSS_V1_9, showtext);
+
+ return (Datum) 0;
+}
+
Datum
pg_stat_statements_1_8(PG_FUNCTION_ARGS)
{
@@ -1642,6 +1657,10 @@ pg_stat_statements_internal(FunctionCallInfo fcinfo,
if (api_version != PGSS_V1_8)
elog(ERROR, "incorrect number of output arguments");
break;
+ case PG_STAT_STATEMENTS_COLS_V1_9:
+ if (api_version != PGSS_V1_9)
+ elog(ERROR, "incorrect number of output arguments");
+ break;
default:
elog(ERROR, "incorrect number of output arguments");
}
@@ -1727,6 +1746,7 @@ pg_stat_statements_internal(FunctionCallInfo fcinfo,
Counters tmp;
double stddev;
int64 queryid = entry->key.queryid;
+ TimestampTz first_seen;
memset(values, 0, sizeof(values));
memset(nulls, 0, sizeof(nulls));
@@ -1793,6 +1813,7 @@ pg_stat_statements_internal(FunctionCallInfo fcinfo,
SpinLockAcquire(&e->mutex);
tmp = e->counters;
+ first_seen = e->first_seen;
SpinLockRelease(&e->mutex);
}
@@ -1864,12 +1885,17 @@ pg_stat_statements_internal(FunctionCallInfo fcinfo,
Int32GetDatum(-1));
values[i++] = wal_bytes;
}
+ if (api_version >= PGSS_V1_9)
+ {
+ values[i++] = TimestampTzGetDatum(first_seen);
+ }
Assert(i == (api_version == PGSS_V1_0 ? PG_STAT_STATEMENTS_COLS_V1_0 :
api_version == PGSS_V1_1 ? PG_STAT_STATEMENTS_COLS_V1_1 :
api_version == PGSS_V1_2 ? PG_STAT_STATEMENTS_COLS_V1_2 :
api_version == PGSS_V1_3 ? PG_STAT_STATEMENTS_COLS_V1_3 :
api_version == PGSS_V1_8 ? PG_STAT_STATEMENTS_COLS_V1_8 :
+ api_version == PGSS_V1_9 ? PG_STAT_STATEMENTS_COLS_V1_9 :
-1 /* fail if you forget to update this assert */ ));
tuplestore_putvalues(tupstore, tupdesc, values, nulls);
@@ -1985,6 +2011,7 @@ entry_alloc(pgssHashKey *key, Size query_offset, int query_len, int encoding,
entry->query_offset = query_offset;
entry->query_len = query_len;
entry->encoding = encoding;
+ entry->first_seen = GetCurrentTimestamp();
}
return entry;
diff --git a/contrib/pg_stat_statements/sql/pg_stat_statements.sql b/contrib/pg_stat_statements/sql/pg_stat_statements.sql
index 6f58d9d0f6..590798d133 100644
--- a/contrib/pg_stat_statements/sql/pg_stat_statements.sql
+++ b/contrib/pg_stat_statements/sql/pg_stat_statements.sql
@@ -364,4 +364,12 @@ SELECT query, plans, calls, rows FROM pg_stat_statements ORDER BY query COLLATE
SELECT pg_stat_statements_reset();
SELECT dealloc FROM pg_stat_statements_info;
+--
+-- statement timestamps
+--
+SELECT pg_stat_statements_reset();
+SELECT now() AS start_ts \gset
+SELECT 1 AS "STMTTS";
+SELECT count(*) FROM pg_stat_statements WHERE first_seen >= :'start_ts' AND query LIKE '%STMTTS%';
+
DROP EXTENSION pg_stat_statements;
diff --git a/doc/src/sgml/pgstatstatements.sgml b/doc/src/sgml/pgstatstatements.sgml
index 464bf0e5ae..54df2ea73a 100644
--- a/doc/src/sgml/pgstatstatements.sgml
+++ b/doc/src/sgml/pgstatstatements.sgml
@@ -363,6 +363,15 @@
Total amount of WAL generated by the statement in bytes
</para></entry>
</row>
+
+ <row>
+ <entry role="catalog_table_entry"><para role="column_definition">
+ <structfield>first_seen</structfield> <type>timestamp with time zone</type>
+ </para>
+ <para>
+ Timestamp of statistics gathering start for the statement
+ </para></entry>
+ </row>
</tbody>
</tgroup>
</table>
