On 11.12.2019 7:26, Kyotaro Horiguchi wrote:
Still I'm not sure non-atomic write is acceptable, but I agree on the
necessity of updating it during a transaction. Couldn't we update
shared stats every n bytes (XLOG_BLCKSZ or such) or every command end?
I think we should refrain from inserting an instruction within the
WALInsertLock section, but I'm not sure which is better between "var
+= var" within the section and "if (inserted) var += var;" outside. If
we can ignore the possitbility of the case where xlogswitch is
omitted, the "if (inserted)" is not needed.
I think that 32-bit Postgres installations are really exotic, but I
agree that showing incorrect result (even with very small probability)
is not acceptable behavior in this case. I attached new versoin of the
patch with use pg_atomic_write_u64 for updating walWritten field.
As far as at 64-bit systems, pg_atomic_write_u64and pg_atomic_read_u64
are translated to ordinary memory access, them should not have some
negative
impact on performance.
--
Konstantin Knizhnik
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 5f0ee50..6a4b209 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -1486,6 +1486,9 @@ CopyXLogRecordToWAL(int write_len, bool isLogSwitch, XLogRecData *rdata,
currpos = GetXLogBuffer(CurrPos);
freespace = INSERT_FREESPACE(CurrPos);
+ /* Accumulate amount of data written to WAL for pg_xact_activity */
+ pg_atomic_write_u64(&MyProc->walWritten, pg_atomic_read_u64(&MyProc->walWritten) + write_len);
+
/*
* there should be enough space for at least the first field (xl_tot_len)
* on this page.
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 000cff3..037d313 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -758,6 +758,9 @@ CREATE VIEW pg_stat_activity AS
LEFT JOIN pg_database AS D ON (S.datid = D.oid)
LEFT JOIN pg_authid AS U ON (S.usesysid = U.oid);
+CREATE VIEW pg_stat_wal_activity AS
+ SELECT a.*,pg_stat_get_wal_activity(a.pid) as wal_written FROM pg_stat_activity a;
+
CREATE VIEW pg_stat_replication AS
SELECT
S.pid,
diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c
index fff0628..c9a63a1 100644
--- a/src/backend/storage/lmgr/proc.c
+++ b/src/backend/storage/lmgr/proc.c
@@ -390,6 +390,8 @@ InitProcess(void)
MyPgXact->xid = InvalidTransactionId;
MyPgXact->xmin = InvalidTransactionId;
MyProc->pid = MyProcPid;
+ pg_atomic_init_u64(&MyProc->walWritten, 0);
+
/* backendId, databaseId and roleId will be filled in later */
MyProc->backendId = InvalidBackendId;
MyProc->databaseId = InvalidOid;
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 05240bf..1745815 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -919,6 +919,22 @@ pg_stat_get_activity(PG_FUNCTION_ARGS)
Datum
+pg_stat_get_wal_activity(PG_FUNCTION_ARGS)
+{
+ int32 pid = PG_GETARG_INT32(0);
+ PGPROC* proc = BackendPidGetProc(pid);
+ if (proc == NULL)
+ {
+ proc = AuxiliaryPidGetProc(pid);
+ }
+ if (proc == NULL)
+ PG_RETURN_NULL();
+ else
+ PG_RETURN_INT64(pg_atomic_read_u64(&proc->walWritten));
+}
+
+
+Datum
pg_backend_pid(PG_FUNCTION_ARGS)
{
PG_RETURN_INT32(MyProcPid);
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index b759b15..6d31afd 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -5152,6 +5152,10 @@
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}',
prosrc => 'pg_stat_get_activity' },
+{ oid => '2121', descr => 'statistics: WAL activity',
+ proname => 'pg_stat_get_wal_activity', provolatile => 's', proisstrict => 't',
+ proparallel => 'r', prorettype => 'int8', proargtypes => 'int4',
+ prosrc => 'pg_stat_get_wal_activity' },
{ oid => '3318',
descr => 'statistics: information about progress of backends running maintenance command',
proname => 'pg_stat_get_progress_info', prorows => '100', proretset => 't',
diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h
index 281e1db..3aa2efb 100644
--- a/src/include/storage/proc.h
+++ b/src/include/storage/proc.h
@@ -203,6 +203,11 @@ struct PGPROC
PGPROC *lockGroupLeader; /* lock group leader, if I'm a member */
dlist_head lockGroupMembers; /* list of members, if I'm a leader */
dlist_node lockGroupLink; /* my member link, if I'm a member */
+
+ /*
+ * Amount of data written to the WAL by this process
+ */
+ pg_atomic_uint64 walWritten;
};
/* NOTE: "typedef struct PGPROC PGPROC" appears in storage/lock.h. */
