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Commit c037471

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anarazelanarazel
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pgstat: Track time of the last scan of a relation
It can be useful to know when a relation has last been used, e.g., when evaluating whether an index is still required. It was already possible to infer the time of the last usage by tracking, e.g., pg_stat_all_indexes.idx_scan over time. But far from everybody does so. To make it easier to detect the last time a relation has been scanned, track that time in each relation's pgstat entry. To minimize overhead a) the timestamp is updated only when the backend pending stats entry is flushed to shared stats b) the last transaction's stop timestamp is used as the timestamp. Bumps catalog and stats format versions. Author: Dave Page <dpage@pgadmin.org> Reviewed-by: Andres Freund <andres@anarazel.de> Reviewed-by: Bruce Momjian <bruce@momjian.us> Reviewed-by: Vik Fearing <vik@postgresfriends.org> Discussion: https://postgr.es/m/CA+OCxozrVHNFVEPkweUHMZje+t1tfY816d9MZYc6eZwOOusOaQ@mail.gmail.com
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‎doc/src/sgml/monitoring.sgml

Copy file name to clipboardExpand all lines: doc/src/sgml/monitoring.sgml
+30Lines changed: 30 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -4385,6 +4385,16 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
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</para></entry>
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</row>
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<row>
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<entry role="catalog_table_entry"><para role="column_definition">
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<structfield>last_seq_scan</structfield> <type>timestamptz</type>
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</para>
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<para>
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The time of the last sequential scan on this table, based on the
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most recent transaction stop time
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</para></entry>
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</row>
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<row>
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<entry role="catalog_table_entry"><para role="column_definition">
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<structfield>seq_tup_read</structfield> <type>bigint</type>
@@ -4403,6 +4413,16 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
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</para></entry>
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</row>
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<row>
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<entry role="catalog_table_entry"><para role="column_definition">
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<structfield>last_idx_scan</structfield> <type>timestamptz</type>
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</para>
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<para>
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The time of the last index scan on this table, based on the
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most recent transaction stop time
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</para></entry>
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</row>
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<row>
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<entry role="catalog_table_entry"><para role="column_definition">
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<structfield>idx_tup_fetch</structfield> <type>bigint</type>
@@ -4654,6 +4674,16 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
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</para></entry>
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</row>
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<row>
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<entry role="catalog_table_entry"><para role="column_definition">
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<structfield>last_idx_scan</structfield> <type>timestamptz</type>
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</para>
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<para>
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The time of the last scan on this index, based on the
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most recent transaction stop time
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</para></entry>
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</row>
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<row>
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<entry role="catalog_table_entry"><para role="column_definition">
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<structfield>idx_tup_read</structfield> <type>bigint</type>

‎src/backend/catalog/system_views.sql

Copy file name to clipboardExpand all lines: src/backend/catalog/system_views.sql
+3Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -656,8 +656,10 @@ CREATE VIEW pg_stat_all_tables AS
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N.nspname AS schemaname,
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C.relname AS relname,
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pg_stat_get_numscans(C.oid) AS seq_scan,
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pg_stat_get_lastscan(C.oid) AS last_seq_scan,
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pg_stat_get_tuples_returned(C.oid) AS seq_tup_read,
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sum(pg_stat_get_numscans(I.indexrelid))::bigint AS idx_scan,
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max(pg_stat_get_lastscan(I.indexrelid)) AS last_idx_scan,
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sum(pg_stat_get_tuples_fetched(I.indexrelid))::bigint +
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pg_stat_get_tuples_fetched(C.oid) AS idx_tup_fetch,
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pg_stat_get_tuples_inserted(C.oid) AS n_tup_ins,
@@ -774,6 +776,7 @@ CREATE VIEW pg_stat_all_indexes AS
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C.relname AS relname,
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I.relname AS indexrelname,
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pg_stat_get_numscans(I.oid) AS idx_scan,
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pg_stat_get_lastscan(I.oid) AS last_idx_scan,
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pg_stat_get_tuples_returned(I.oid) AS idx_tup_read,
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pg_stat_get_tuples_fetched(I.oid) AS idx_tup_fetch
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FROM pg_class C JOIN

‎src/backend/utils/activity/pgstat_relation.c

Copy file name to clipboardExpand all lines: src/backend/utils/activity/pgstat_relation.c
+6Lines changed: 6 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -789,6 +789,12 @@ pgstat_relation_flush_cb(PgStat_EntryRef *entry_ref, bool nowait)
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tabentry = &shtabstats->stats;
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tabentry->numscans += lstats->t_counts.t_numscans;
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if (lstats->t_counts.t_numscans)
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{
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TimestampTz t = GetCurrentTransactionStopTimestamp();
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if (t > tabentry->lastscan)
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tabentry->lastscan = t;
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}
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tabentry->tuples_returned += lstats->t_counts.t_tuples_returned;
793799
tabentry->tuples_fetched += lstats->t_counts.t_tuples_fetched;
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tabentry->tuples_inserted += lstats->t_counts.t_tuples_inserted;

‎src/backend/utils/adt/pgstatfuncs.c

Copy file name to clipboardExpand all lines: src/backend/utils/adt/pgstatfuncs.c
+13Lines changed: 13 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -52,6 +52,19 @@ pg_stat_get_numscans(PG_FUNCTION_ARGS)
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}
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Datum
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pg_stat_get_lastscan(PG_FUNCTION_ARGS)
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{
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Oid relid = PG_GETARG_OID(0);
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PgStat_StatTabEntry *tabentry;
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if ((tabentry = pgstat_fetch_stat_tabentry(relid)) == NULL)
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PG_RETURN_NULL();
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else
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PG_RETURN_TIMESTAMPTZ(tabentry->lastscan);
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}
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Datum
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pg_stat_get_tuples_returned(PG_FUNCTION_ARGS)
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{

‎src/include/catalog/catversion.h

Copy file name to clipboardExpand all lines: src/include/catalog/catversion.h
+1-1Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -57,6 +57,6 @@
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*/
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/* yyyymmddN */
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#define CATALOG_VERSION_NO 202209291
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#define CATALOG_VERSION_NO 202210141
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#endif

‎src/include/catalog/pg_proc.dat

Copy file name to clipboardExpand all lines: src/include/catalog/pg_proc.dat
+4Lines changed: 4 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -5252,6 +5252,10 @@
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proname => 'pg_stat_get_numscans', provolatile => 's', proparallel => 'r',
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prorettype => 'int8', proargtypes => 'oid',
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prosrc => 'pg_stat_get_numscans' },
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{ oid => '9976', descr => 'statistics: time of the last scan for table/index',
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proname => 'pg_stat_get_lastscan', provolatile => 's', proparallel => 'r',
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prorettype => 'timestamptz', proargtypes => 'oid',
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prosrc => 'pg_stat_get_lastscan' },
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{ oid => '1929', descr => 'statistics: number of tuples read by seqscan',
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proname => 'pg_stat_get_tuples_returned', provolatile => 's',
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proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',

‎src/include/pgstat.h

Copy file name to clipboardExpand all lines: src/include/pgstat.h
+2-1Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -242,7 +242,7 @@ typedef struct PgStat_TableXactStatus
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* ------------------------------------------------------------
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*/
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#define PGSTAT_FILE_FORMAT_ID 0x01A5BCA8
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#define PGSTAT_FILE_FORMAT_ID 0x01A5BCA9
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typedef struct PgStat_ArchiverStats
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{
@@ -354,6 +354,7 @@ typedef struct PgStat_StatSubEntry
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typedef struct PgStat_StatTabEntry
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{
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PgStat_Counter numscans;
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TimestampTz lastscan;
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PgStat_Counter tuples_returned;
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PgStat_Counter tuples_fetched;

‎src/test/regress/expected/rules.out

Copy file name to clipboardExpand all lines: src/test/regress/expected/rules.out
+9Lines changed: 9 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1763,6 +1763,7 @@ pg_stat_all_indexes| SELECT c.oid AS relid,
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c.relname,
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i.relname AS indexrelname,
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pg_stat_get_numscans(i.oid) AS idx_scan,
1766+
pg_stat_get_lastscan(i.oid) AS last_idx_scan,
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pg_stat_get_tuples_returned(i.oid) AS idx_tup_read,
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pg_stat_get_tuples_fetched(i.oid) AS idx_tup_fetch
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FROM (((pg_class c
@@ -1774,8 +1775,10 @@ pg_stat_all_tables| SELECT c.oid AS relid,
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n.nspname AS schemaname,
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c.relname,
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pg_stat_get_numscans(c.oid) AS seq_scan,
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pg_stat_get_lastscan(c.oid) AS last_seq_scan,
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pg_stat_get_tuples_returned(c.oid) AS seq_tup_read,
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(sum(pg_stat_get_numscans(i.indexrelid)))::bigint AS idx_scan,
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max(pg_stat_get_lastscan(i.indexrelid)) AS last_idx_scan,
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((sum(pg_stat_get_tuples_fetched(i.indexrelid)))::bigint + pg_stat_get_tuples_fetched(c.oid)) AS idx_tup_fetch,
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pg_stat_get_tuples_inserted(c.oid) AS n_tup_ins,
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pg_stat_get_tuples_updated(c.oid) AS n_tup_upd,
@@ -2107,6 +2110,7 @@ pg_stat_sys_indexes| SELECT pg_stat_all_indexes.relid,
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pg_stat_all_indexes.relname,
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pg_stat_all_indexes.indexrelname,
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pg_stat_all_indexes.idx_scan,
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pg_stat_all_indexes.last_idx_scan,
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pg_stat_all_indexes.idx_tup_read,
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pg_stat_all_indexes.idx_tup_fetch
21122116
FROM pg_stat_all_indexes
@@ -2115,8 +2119,10 @@ pg_stat_sys_tables| SELECT pg_stat_all_tables.relid,
21152119
pg_stat_all_tables.schemaname,
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pg_stat_all_tables.relname,
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pg_stat_all_tables.seq_scan,
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pg_stat_all_tables.last_seq_scan,
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pg_stat_all_tables.seq_tup_read,
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pg_stat_all_tables.idx_scan,
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pg_stat_all_tables.last_idx_scan,
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pg_stat_all_tables.idx_tup_fetch,
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pg_stat_all_tables.n_tup_ins,
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pg_stat_all_tables.n_tup_upd,
@@ -2151,6 +2157,7 @@ pg_stat_user_indexes| SELECT pg_stat_all_indexes.relid,
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pg_stat_all_indexes.relname,
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pg_stat_all_indexes.indexrelname,
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pg_stat_all_indexes.idx_scan,
2160+
pg_stat_all_indexes.last_idx_scan,
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pg_stat_all_indexes.idx_tup_read,
21552162
pg_stat_all_indexes.idx_tup_fetch
21562163
FROM pg_stat_all_indexes
@@ -2159,8 +2166,10 @@ pg_stat_user_tables| SELECT pg_stat_all_tables.relid,
21592166
pg_stat_all_tables.schemaname,
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pg_stat_all_tables.relname,
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pg_stat_all_tables.seq_scan,
2169+
pg_stat_all_tables.last_seq_scan,
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pg_stat_all_tables.seq_tup_read,
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pg_stat_all_tables.idx_scan,
2172+
pg_stat_all_tables.last_idx_scan,
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pg_stat_all_tables.idx_tup_fetch,
21652174
pg_stat_all_tables.n_tup_ins,
21662175
pg_stat_all_tables.n_tup_upd,

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