Re: [PATCH] Unremovable tuple monitoring (was: Addition of some trivial auto vacuum logging)

On 28/09/2011, at 11:17 AM, Tom Lane wrote:

> Alvaro Herrera <alvherre(at)commandprompt(dot)com> writes:
>> Excerpts from Royce Ausburn's message of mar sep 27 21:28:26 -0300 2011:
>>> Tom's suggestion looks like it's less trivial that I can do just yet, but I'll take a look and ask for help if I need it.
>
>> It's not that difficult. Just do a search on "git log
>> src/backend/postmaster/pgstat.c" for patches that add a new column
>> somewhere.
>
> Yeah, I was just about to say the same thing. Find a previous patch
> that adds a feature similar to what you have in mind, and crib like mad.
> We've added enough stats counters over time that you should have several
> models to work from.

This patch does as Tom suggested, adding a column to the pg_stat_all_tables view which exposes the number of unremovable tuples in the last vacuum. This patch does not include my previous work to log this information as part of auto_vacuum's logging.

User visible additions:
New column pg_stat_all_tables.n_unremovable_tup
New function bigint pg_stat_get_unremovable_tuples(oid)

A few notes / questions:

- I'm not sure if I'm supposed to update CATALOG_VERSION_NO in catalog.h. In this patch I have.

- I'm not sure about how I should be selecting an OID for my new stats function. I used the unused_oids script and picked one that seemed reasonable.

- The VACUUM FULL implementation in cluster.c doesn't do any stats updating similar to vacuumlazy.c, so I haven't don't anything there… (is this right? A vacuum full may also encounter unremovable tuples, right?)

- I'm not usually a C developer, so peeps reviewing please watch for noob mistakes.

Cheers,

--Royce

diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index a19e3f0..af7b235 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -328,7 +328,8 @@ postgres: <replaceable>user</> <replaceable>database</> <replaceable>host</> <re
belonging to the table), number of live rows fetched by index
scans, numbers of row insertions, updates, and deletions,
number of row updates that were HOT (i.e., no separate index update),
- numbers of live and dead rows,
+ numbers of live and dead rows,
+ the number of dead tuples not removed in the last vacuum,
the last time the table was non-<option>FULL</> vacuumed manually,
the last time it was vacuumed by the autovacuum daemon,
the last time it was analyzed manually,
@@ -764,6 +765,14 @@ postgres: <replaceable>user</> <replaceable>database</> <replaceable>host</> <re
Number of dead rows in table
</entry>
</row>
+
+ <row>
+ <entry><literal><function>pg_stat_get_unremovable_tuples</function>(<type>oid</type>)</literal></entry>
+ <entry><type>bigint</type></entry>
+ <entry>
+ Number of dead rows not removed in the table's last vacuum
+ </entry>
+ </row>

<row>
<entry><literal><function>pg_stat_get_blocks_fetched</function>(<type>oid</type>)</literal></entry>
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 2253ca8..9c18dc7 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -353,6 +353,7 @@ CREATE VIEW pg_stat_all_tables AS
pg_stat_get_tuples_hot_updated(C.oid) AS n_tup_hot_upd,
pg_stat_get_live_tuples(C.oid) AS n_live_tup,
pg_stat_get_dead_tuples(C.oid) AS n_dead_tup,
+ pg_stat_get_unremovable_tuples(C.oid) AS n_unremovable_tup,
pg_stat_get_last_vacuum_time(C.oid) as last_vacuum,
pg_stat_get_last_autovacuum_time(C.oid) as last_autovacuum,
pg_stat_get_last_analyze_time(C.oid) as last_analyze,
diff --git a/src/backend/commands/vacuumlazy.c b/src/backend/commands/vacuumlazy.c
index cf8337b..140fe92 100644
--- a/src/backend/commands/vacuumlazy.c
+++ b/src/backend/commands/vacuumlazy.c
@@ -91,6 +91,7 @@ typedef struct LVRelStats
double scanned_tuples; /* counts only tuples on scanned pages */
double old_rel_tuples; /* previous value of pg_class.reltuples */
double new_rel_tuples; /* new estimated total # of tuples */
+ double unremovable_tuples; /* count of dead tuples not yet removable */
BlockNumber pages_removed;
double tuples_deleted;
BlockNumber nonempty_pages; /* actually, last nonempty page + 1 */
@@ -245,7 +246,8 @@ lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt,
/* report results to the stats collector, too */
pgstat_report_vacuum(RelationGetRelid(onerel),
onerel->rd_rel->relisshared,
- new_rel_tuples);
+ new_rel_tuples,
+ vacrelstats->unremovable_tuples);

/* and log the action if appropriate */
if (IsAutoVacuumWorkerProcess() && Log_autovacuum_min_duration >= 0)
@@ -829,6 +831,7 @@ lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats,
/* save stats for use later */
vacrelstats->scanned_tuples = num_tuples;
vacrelstats->tuples_deleted = tups_vacuumed;
+ vacrelstats->unremovable_tuples = nkeep;

/* now we can compute the new value for pg_class.reltuples */
vacrelstats->new_rel_tuples = vac_estimate_reltuples(onerel, false,
diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c
index 9132db7..40d1107 100644
--- a/src/backend/postmaster/pgstat.c
+++ b/src/backend/postmaster/pgstat.c
@@ -1251,7 +1251,7 @@ pgstat_report_autovac(Oid dboid)
* ---------
*/
void
-pgstat_report_vacuum(Oid tableoid, bool shared, PgStat_Counter tuples)
+pgstat_report_vacuum(Oid tableoid, bool shared, PgStat_Counter tuples, PgStat_Counter m_unremovable_tuples)
{
PgStat_MsgVacuum msg;

@@ -1264,6 +1264,7 @@ pgstat_report_vacuum(Oid tableoid, bool shared, PgStat_Counter tuples)
msg.m_autovacuum = IsAutoVacuumWorkerProcess();
msg.m_vacuumtime = GetCurrentTimestamp();
msg.m_tuples = tuples;
+ msg.m_unremovable_tuples = m_unremovable_tuples;
pgstat_send(&msg, sizeof(msg));
}

@@ -4202,6 +4203,7 @@ pgstat_recv_vacuum(PgStat_MsgVacuum *msg, int len)
tabentry = pgstat_get_tab_entry(dbentry, msg->m_tableoid, true);

tabentry->n_live_tuples = msg->m_tuples;
+ tabentry->n_unremovable_tuples = msg->m_unremovable_tuples;
/* Resetting dead_tuples to 0 is an approximation ... */
tabentry->n_dead_tuples = 0;

diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 7792b33..fb60fc5 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -33,6 +33,7 @@ extern Datum pg_stat_get_tuples_deleted(PG_FUNCTION_ARGS);
extern Datum pg_stat_get_tuples_hot_updated(PG_FUNCTION_ARGS);
extern Datum pg_stat_get_live_tuples(PG_FUNCTION_ARGS);
extern Datum pg_stat_get_dead_tuples(PG_FUNCTION_ARGS);
+extern Datum pg_stat_get_unremovable_tuples(PG_FUNCTION_ARGS);
extern Datum pg_stat_get_blocks_fetched(PG_FUNCTION_ARGS);
extern Datum pg_stat_get_blocks_hit(PG_FUNCTION_ARGS);
extern Datum pg_stat_get_last_vacuum_time(PG_FUNCTION_ARGS);
@@ -256,6 +257,22 @@ pg_stat_get_dead_tuples(PG_FUNCTION_ARGS)
PG_RETURN_INT64(result);
}

+Datum
+pg_stat_get_unremovable_tuples(PG_FUNCTION_ARGS)
+{
+ Oid relid = PG_GETARG_OID(0);
+ int64 result;
+ PgStat_StatTabEntry *tabentry;
+
+ if ((tabentry = pgstat_fetch_stat_tabentry(relid)) == NULL)
+ result = 0;
+ else
+ result = (int64) (tabentry->n_unremovable_tuples);
+
+ PG_RETURN_INT64(result);
+}
+
+

Datum
pg_stat_get_blocks_fetched(PG_FUNCTION_ARGS)
diff --git a/src/include/catalog/catversion.h b/src/include/catalog/catversion.h
index f3c8bb4..950f1f2 100644
--- a/src/include/catalog/catversion.h
+++ b/src/include/catalog/catversion.h
@@ -53,6 +53,6 @@
*/

/* yyyymmddN */
-#define CATALOG_VERSION_NO 201109071
+#define CATALOG_VERSION_NO 201110031

#endif
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index 96f43fe..69f6415 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -2526,6 +2526,8 @@ DATA(insert OID = 2878 ( pg_stat_get_live_tuples PGNSP PGUID 12 1 0 0 0 f f f t
DESCR("statistics: number of live tuples");
DATA(insert OID = 2879 ( pg_stat_get_dead_tuples PGNSP PGUID 12 1 0 0 0 f f f t f s 1 0 20 "26" _null_ _null_ _null_ _null_ pg_stat_get_dead_tuples _null_ _null_ _null_ ));
DESCR("statistics: number of dead tuples");
+DATA(insert OID = 3122 ( pg_stat_get_unremovable_tuples PGNSP PGUID 12 1 0 0 0 f f f t f s 1 0 20 "26" _null_ _null_ _null_ _null_ pg_stat_get_unremovable_tuples _null_ _null_ _null_ ));
+DESCR("statistics: number of dead tuples not yet removable");
DATA(insert OID = 1934 ( pg_stat_get_blocks_fetched PGNSP PGUID 12 1 0 0 0 f f f t f s 1 0 20 "26" _null_ _null_ _null_ _null_ pg_stat_get_blocks_fetched _null_ _null_ _null_ ));
DESCR("statistics: number of blocks fetched");
DATA(insert OID = 1935 ( pg_stat_get_blocks_hit PGNSP PGUID 12 1 0 0 0 f f f t f s 1 0 20 "26" _null_ _null_ _null_ _null_ pg_stat_get_blocks_hit _null_ _null_ _null_ ));
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index 20c4d43..e1b082e 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -326,6 +326,7 @@ typedef struct PgStat_MsgVacuum
bool m_autovacuum;
TimestampTz m_vacuumtime;
PgStat_Counter m_tuples;
+ PgStat_Counter m_unremovable_tuples;
} PgStat_MsgVacuum;


@@ -539,6 +540,7 @@ typedef struct PgStat_StatTabEntry

PgStat_Counter n_live_tuples;
PgStat_Counter n_dead_tuples;
+ PgStat_Counter n_unremovable_tuples;
PgStat_Counter changes_since_analyze;

PgStat_Counter blocks_fetched;
@@ -706,7 +708,7 @@ extern void pgstat_reset_single_counter(Oid objectid, PgStat_Single_Reset_Type t

extern void pgstat_report_autovac(Oid dboid);
extern void pgstat_report_vacuum(Oid tableoid, bool shared,
- PgStat_Counter tuples);
+ PgStat_Counter tuples, PgStat_Counter unremovable_tuples);
extern void pgstat_report_analyze(Relation rel,
PgStat_Counter livetuples, PgStat_Counter deadtuples);