On Thu, Dec 26, 2019 at 9:08 AM Guillaume Lelarge
<[email protected]> wrote:
>
> Le mer. 25 déc. 2019 à 19:30, Julien Rouhaud <[email protected]> a écrit :
>>
>> On Wed, Dec 25, 2019 at 7:03 PM Julien Rouhaud <[email protected]> wrote:
>> >
>> > Guillaume (in Cc) recently pointed out [1] that it's currently not
>> > possible to retrieve the list of parallel workers for a given backend
>> > at the SQL level. His use case was to develop a function in plpgsql
>> > to sample a given query wait event, but it's not hard to imagine other
>> > useful use cases for this information, for instance doing some
>> > analysis on the average number of workers per parallel query, or ratio
>> > of parallel queries. IIUC parallel queries is for now the only user
>> > of lock group, so this should work just fine.
>> >
>> > I'm attaching a trivial patch to expose the group leader pid if any
>> > in pg_stat_activity. Quick example of usage:
>> >
>> > =# SELECT query, leader_pid,
>> > array_agg(pid) filter(WHERE leader_pid != pid) AS members
>> > FROM pg_stat_activity
>> > WHERE leader_pid IS NOT NULL
>> > GROUP BY query, leader_pid;
>> > query | leader_pid | members
>> > -------------------+------------+---------------
>> > select * from t1; | 28701 | {28728,28732}
>> > (1 row)
>> >
>> >
>> > [1] https://twitter.com/g_lelarge/status/1209486212190343168
>>
>> And I just realized that I forgot to update rule.out, sorry about
>> that. v2 attached.
>
>
> So I tried your patch this morning, and it works really well.
>
> On a SELECT count(*), I got this:
>
> SELECT leader_pid, pid, wait_event_type, wait_event, state, backend_type FROM
> pg_stat_activity WHERE pid=111439 or leader_pid=111439;
>
> ┌────────────┬────────┬─────────────────┬──────────────┬────────┬─────────────────┐
> │ leader_pid │ pid │ wait_event_type │ wait_event │ state │
> backend_type │
> ├────────────┼────────┼─────────────────┼──────────────┼────────┼─────────────────┤
> │ 111439 │ 111439 │ LWLock │ WALWriteLock │ active │ client
> backend │
> │ 111439 │ 116887 │ LWLock │ WALWriteLock │ active │ parallel
> worker │
> │ 111439 │ 116888 │ IO │ WALSync │ active │ parallel
> worker │
> └────────────┴────────┴─────────────────┴──────────────┴────────┴─────────────────┘
> (3 rows)
>
> and this from a CREATE INDEX:
>
> ┌────────────┬────────┬─────────────────┬────────────┬────────┬─────────────────┐
> │ leader_pid │ pid │ wait_event_type │ wait_event │ state │ backend_type
> │
> ├────────────┼────────┼─────────────────┼────────────┼────────┼─────────────────┤
> │ 111439 │ 111439 │ │ │ active │ client
> backend │
> │ 111439 │ 118775 │ │ │ active │ parallel
> worker │
> └────────────┴────────┴─────────────────┴────────────┴────────┴─────────────────┘
> (2 rows)
>
> Anyway, it applies cleanly, it compiles, and it works. Documentation is
> available. So it looks to me it's good to go :)
Thanks for the review Guillaume. Double checking the doc, I see that
I made a copy/pasto mistake in the new field name. Attached v3 should
be all good.
diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index dcb58115af..a64959b600 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -614,6 +614,11 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
<entry><type>integer</type></entry>
<entry>Process ID of this backend</entry>
</row>
+ <row>
+ <entry><structfield>leader_pid</structfield></entry>
+ <entry><type>integer</type></entry>
+ <entry>Process ID of the lock group leader, if any</entry>
+ </row>
<row>
<entry><structfield>usesysid</structfield></entry>
<entry><type>oid</type></entry>
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index f7800f01a6..0c3eb08028 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -734,6 +734,7 @@ CREATE VIEW pg_stat_activity AS
S.datid AS datid,
D.datname AS datname,
S.pid,
+ S.leader_pid,
S.usesysid,
U.rolname AS usename,
S.application_name,
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index d9f78221aa..323eb89c86 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -545,7 +545,7 @@ pg_stat_get_progress_info(PG_FUNCTION_ARGS)
Datum
pg_stat_get_activity(PG_FUNCTION_ARGS)
{
-#define PG_STAT_GET_ACTIVITY_COLS 29
+#define PG_STAT_GET_ACTIVITY_COLS 30
int num_backends = pgstat_fetch_stat_numbackends();
int curr_backend;
int pid = PG_ARGISNULL(0) ? -1 : PG_GETARG_INT32(0);
@@ -684,6 +684,7 @@ pg_stat_get_activity(PG_FUNCTION_ARGS)
values[5] = CStringGetTextDatum(clipped_activity);
pfree(clipped_activity);
+ nulls[29] = true;
proc = BackendPidGetProc(beentry->st_procpid);
if (proc != NULL)
{
@@ -693,6 +694,12 @@ pg_stat_get_activity(PG_FUNCTION_ARGS)
wait_event_type = pgstat_get_wait_event_type(raw_wait_event);
wait_event = pgstat_get_wait_event(raw_wait_event);
+ if (proc->lockGroupLeader)
+ {
+ values[29] = Int32GetDatum(proc->lockGroupLeader->pid);
+ nulls[29] = false;
+ }
+
}
else if (beentry->st_backendType != B_BACKEND)
{
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index ac8f64b219..6ff7322425 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -5148,9 +5148,9 @@
proname => 'pg_stat_get_activity', prorows => '100', proisstrict => 'f',
proretset => 't', provolatile => 's', proparallel => 'r',
prorettype => 'record', proargtypes => 'int4',
- proallargtypes => '{int4,oid,int4,oid,text,text,text,text,text,timestamptz,timestamptz,timestamptz,timestamptz,inet,text,int4,xid,xid,text,bool,text,text,int4,bool,text,numeric,text,bool,text,bool}',
- proargmodes => '{i,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o}',
- proargnames => '{pid,datid,pid,usesysid,application_name,state,query,wait_event_type,wait_event,xact_start,query_start,backend_start,state_change,client_addr,client_hostname,client_port,backend_xid,backend_xmin,backend_type,ssl,sslversion,sslcipher,sslbits,sslcompression,ssl_client_dn,ssl_client_serial,ssl_issuer_dn,gss_auth,gss_princ,gss_enc}',
+ proallargtypes => '{int4,oid,int4,oid,text,text,text,text,text,timestamptz,timestamptz,timestamptz,timestamptz,inet,text,int4,xid,xid,text,bool,text,text,int4,bool,text,numeric,text,bool,text,bool,int4}',
+ proargmodes => '{i,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o}',
+ proargnames => '{pid,datid,pid,usesysid,application_name,state,query,wait_event_type,wait_event,xact_start,query_start,backend_start,state_change,client_addr,client_hostname,client_port,backend_xid,backend_xmin,backend_type,ssl,sslversion,sslcipher,sslbits,sslcompression,ssl_client_dn,ssl_client_serial,ssl_issuer_dn,gss_auth,gss_princ,gss_enc,leader_pid}',
prosrc => 'pg_stat_get_activity' },
{ oid => '3318',
descr => 'statistics: information about progress of backends running maintenance command',
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index 80a07825b9..02200c46c4 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -1724,6 +1724,7 @@ pg_shadow| SELECT pg_authid.rolname AS usename,
pg_stat_activity| SELECT s.datid,
d.datname,
s.pid,
+ s.leader_pid,
s.usesysid,
u.rolname AS usename,
s.application_name,
@@ -1741,7 +1742,7 @@ pg_stat_activity| SELECT s.datid,
s.backend_xmin,
s.query,
s.backend_type
- FROM ((pg_stat_get_activity(NULL::integer) s(datid, pid, usesysid, application_name, state, query, wait_event_type, wait_event, xact_start, query_start, backend_start, state_change, client_addr, client_hostname, client_port, backend_xid, backend_xmin, backend_type, ssl, sslversion, sslcipher, sslbits, sslcompression, ssl_client_dn, ssl_client_serial, ssl_issuer_dn, gss_auth, gss_princ, gss_enc)
+ FROM ((pg_stat_get_activity(NULL::integer) s(datid, pid, usesysid, application_name, state, query, wait_event_type, wait_event, xact_start, query_start, backend_start, state_change, client_addr, client_hostname, client_port, backend_xid, backend_xmin, backend_type, ssl, sslversion, sslcipher, sslbits, sslcompression, ssl_client_dn, ssl_client_serial, ssl_issuer_dn, gss_auth, gss_princ, gss_enc, leader_pid)
LEFT JOIN pg_database d ON ((s.datid = d.oid)))
LEFT JOIN pg_authid u ON ((s.usesysid = u.oid)));
pg_stat_all_indexes| SELECT c.oid AS relid,
@@ -1845,7 +1846,7 @@ pg_stat_gssapi| SELECT s.pid,
s.gss_auth AS gss_authenticated,
s.gss_princ AS principal,
s.gss_enc AS encrypted
- FROM pg_stat_get_activity(NULL::integer) s(datid, pid, usesysid, application_name, state, query, wait_event_type, wait_event, xact_start, query_start, backend_start, state_change, client_addr, client_hostname, client_port, backend_xid, backend_xmin, backend_type, ssl, sslversion, sslcipher, sslbits, sslcompression, ssl_client_dn, ssl_client_serial, ssl_issuer_dn, gss_auth, gss_princ, gss_enc)
+ FROM pg_stat_get_activity(NULL::integer) s(datid, pid, usesysid, application_name, state, query, wait_event_type, wait_event, xact_start, query_start, backend_start, state_change, client_addr, client_hostname, client_port, backend_xid, backend_xmin, backend_type, ssl, sslversion, sslcipher, sslbits, sslcompression, ssl_client_dn, ssl_client_serial, ssl_issuer_dn, gss_auth, gss_princ, gss_enc, leader_pid)
WHERE (s.client_port IS NOT NULL);
pg_stat_progress_cluster| SELECT s.pid,
s.datid,
@@ -1956,7 +1957,7 @@ pg_stat_replication| SELECT s.pid,
w.spill_txns,
w.spill_count,
w.spill_bytes
- FROM ((pg_stat_get_activity(NULL::integer) s(datid, pid, usesysid, application_name, state, query, wait_event_type, wait_event, xact_start, query_start, backend_start, state_change, client_addr, client_hostname, client_port, backend_xid, backend_xmin, backend_type, ssl, sslversion, sslcipher, sslbits, sslcompression, ssl_client_dn, ssl_client_serial, ssl_issuer_dn, gss_auth, gss_princ, gss_enc)
+ FROM ((pg_stat_get_activity(NULL::integer) s(datid, pid, usesysid, application_name, state, query, wait_event_type, wait_event, xact_start, query_start, backend_start, state_change, client_addr, client_hostname, client_port, backend_xid, backend_xmin, backend_type, ssl, sslversion, sslcipher, sslbits, sslcompression, ssl_client_dn, ssl_client_serial, ssl_issuer_dn, gss_auth, gss_princ, gss_enc, leader_pid)
JOIN pg_stat_get_wal_senders() w(pid, state, sent_lsn, write_lsn, flush_lsn, replay_lsn, write_lag, flush_lag, replay_lag, sync_priority, sync_state, reply_time, spill_txns, spill_count, spill_bytes) ON ((s.pid = w.pid)))
LEFT JOIN pg_authid u ON ((s.usesysid = u.oid)));
pg_stat_ssl| SELECT s.pid,
@@ -1968,7 +1969,7 @@ pg_stat_ssl| SELECT s.pid,
s.ssl_client_dn AS client_dn,
s.ssl_client_serial AS client_serial,
s.ssl_issuer_dn AS issuer_dn
- FROM pg_stat_get_activity(NULL::integer) s(datid, pid, usesysid, application_name, state, query, wait_event_type, wait_event, xact_start, query_start, backend_start, state_change, client_addr, client_hostname, client_port, backend_xid, backend_xmin, backend_type, ssl, sslversion, sslcipher, sslbits, sslcompression, ssl_client_dn, ssl_client_serial, ssl_issuer_dn, gss_auth, gss_princ, gss_enc)
+ FROM pg_stat_get_activity(NULL::integer) s(datid, pid, usesysid, application_name, state, query, wait_event_type, wait_event, xact_start, query_start, backend_start, state_change, client_addr, client_hostname, client_port, backend_xid, backend_xmin, backend_type, ssl, sslversion, sslcipher, sslbits, sslcompression, ssl_client_dn, ssl_client_serial, ssl_issuer_dn, gss_auth, gss_princ, gss_enc, leader_pid)
WHERE (s.client_port IS NOT NULL);
pg_stat_subscription| SELECT su.oid AS subid,
su.subname,
