On 2020-01-10 04:32, Masahiko Sawada wrote:
I agreed that these patches are useful on its own and 0001 patch and
committed 0001
0002 patch look good to me. For 0003 patch,
+ linkend="guc-primary-slot-name"/>. Otherwise, the WAL receiver may use
+ a temporary replication slot (determined by <xref
+ linkend="guc-wal-receiver-create-temp-slot"/>), but these are not shown
+ here.
I think it's better to show the temporary slot name on
pg_stat_wal_receiver view. Otherwise user would have no idea about
what wal receiver is using the temporary slot.
Makes sense. It makes the code a bit more fiddly, but it seems worth
it. New patches attached.
--
Peter Eisentraut http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
From 2a089e6bd34b04e17f7b2918057d8e8eb04c117f Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <pe...@eisentraut.org>
Date: Sat, 11 Jan 2020 10:22:08 +0100
Subject: [PATCH v2 1/2] Expose PQbackendPID() through walreceiver API
This will be used by a subsequent patch.
---
.../replication/libpqwalreceiver/libpqwalreceiver.c | 11 +++++++++++
src/include/replication/walreceiver.h | 4 ++++
2 files changed, 15 insertions(+)
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 658af71fec..b731d3fd04 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -74,6 +74,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
bool
temporary,
CRSSnapshotAction snapshot_action,
XLogRecPtr
*lsn);
+static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
const char *query,
const int nRetTypes,
@@ -93,6 +94,7 @@ static WalReceiverFunctionsType PQWalReceiverFunctions = {
libpqrcv_receive,
libpqrcv_send,
libpqrcv_create_slot,
+ libpqrcv_get_backend_pid,
libpqrcv_exec,
libpqrcv_disconnect
};
@@ -858,6 +860,15 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char
*slotname,
return snapshot;
}
+/*
+ * Return PID of remote backend process.
+ */
+static pid_t
+libpqrcv_get_backend_pid(WalReceiverConn *conn)
+{
+ return PQbackendPID(conn->streamConn);
+}
+
/*
* Convert tuple query result to tuplestore.
*/
diff --git a/src/include/replication/walreceiver.h
b/src/include/replication/walreceiver.h
index a276237477..172cfa2862 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -226,6 +226,7 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn
*conn,
const char *slotname, bool temporary,
CRSSnapshotAction snapshot_action,
XLogRecPtr *lsn);
+typedef pid_t (*walrcv_get_backend_pid_fn) (WalReceiverConn *conn);
typedef WalRcvExecResult *(*walrcv_exec_fn) (WalReceiverConn *conn,
const char *query,
const int nRetTypes,
@@ -246,6 +247,7 @@ typedef struct WalReceiverFunctionsType
walrcv_receive_fn walrcv_receive;
walrcv_send_fn walrcv_send;
walrcv_create_slot_fn walrcv_create_slot;
+ walrcv_get_backend_pid_fn walrcv_get_backend_pid;
walrcv_exec_fn walrcv_exec;
walrcv_disconnect_fn walrcv_disconnect;
} WalReceiverFunctionsType;
@@ -276,6 +278,8 @@ extern PGDLLIMPORT WalReceiverFunctionsType
*WalReceiverFunctions;
WalReceiverFunctions->walrcv_send(conn, buffer, nbytes)
#define walrcv_create_slot(conn, slotname, temporary, snapshot_action, lsn) \
WalReceiverFunctions->walrcv_create_slot(conn, slotname, temporary,
snapshot_action, lsn)
+#define walrcv_get_backend_pid(conn) \
+ WalReceiverFunctions->walrcv_get_backend_pid(conn)
#define walrcv_exec(conn, exec, nRetTypes, retTypes) \
WalReceiverFunctions->walrcv_exec(conn, exec, nRetTypes, retTypes)
#define walrcv_disconnect(conn) \
--
2.24.1
From c6ebd1275f8e2490c8a1a5dba981bdce53aafe20 Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <pe...@eisentraut.org>
Date: Sat, 11 Jan 2020 10:24:49 +0100
Subject: [PATCH v2 2/2] walreceiver uses a temporary replication slot by
default
If no permanent replication slot is configured using
primary_slot_name, the walreceiver now creates and uses a temporary
replication slot. A new setting wal_receiver_create_temp_slot can be
used to disable this behavior, for example, if the remote instance is
out of replication slots.
---
doc/src/sgml/config.sgml | 20 +++++++++
doc/src/sgml/monitoring.sgml | 9 +++-
.../libpqwalreceiver/libpqwalreceiver.c | 4 ++
src/backend/replication/walreceiver.c | 41 +++++++++++++++++++
src/backend/utils/misc/guc.c | 9 ++++
src/backend/utils/misc/postgresql.conf.sample | 1 +
src/include/replication/walreceiver.h | 7 ++++
7 files changed, 90 insertions(+), 1 deletion(-)
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 5d1c90282f..5d45b6f7cb 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4124,6 +4124,26 @@ <title>Standby Servers</title>
</listitem>
</varlistentry>
+ <varlistentry id="guc-wal-receiver-create-temp-slot"
xreflabel="wal_receiver_create_temp_slot">
+ <term><varname>wal_receiver_create_temp_slot</varname>
(<type>boolean</type>)
+ <indexterm>
+ <primary><varname>wal_receiver_create_temp_slot</varname> configuration
parameter</primary>
+ </indexterm>
+ </term>
+ <listitem>
+ <para>
+ Specifies whether a WAL receiver should create a temporary replication
+ slot on the remote instance when no permanent replication slot to use
+ has been configured (using <xref linkend="guc-primary-slot-name"/>).
+ The default is on. The only reason to turn this off would be if the
+ remote instance is currently out of available replication slots. This
+ parameter can only be set in the <filename>postgresql.conf</filename>
+ file or on the server command line. Changes only take effect when the
+ WAL receiver process starts a new connection.
+ </para>
+ </listitem>
+ </varlistentry>
+
<varlistentry id="guc-wal-receiver-status-interval"
xreflabel="wal_receiver_status_interval">
<term><varname>wal_receiver_status_interval</varname>
(<type>integer</type>)
<indexterm>
diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index dcb58115af..a2f5bbae66 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -2117,7 +2117,14 @@ <title><structname>pg_stat_wal_receiver</structname>
View</title>
<row>
<entry><structfield>slot_name</structfield></entry>
<entry><type>text</type></entry>
- <entry>Replication slot name used by this WAL receiver</entry>
+ <entry>
+ Replication slot name used by this WAL receiver. This is only set if a
+ permanent replication slot is set using <xref
+ linkend="guc-primary-slot-name"/>. Otherwise, the WAL receiver may use
+ a temporary replication slot (determined by <xref
+ linkend="guc-wal-receiver-create-temp-slot"/>), but these are not shown
+ here.
+ </entry>
</row>
<row>
<entry><structfield>sender_host</structfield></entry>
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index b731d3fd04..e4fd1f9bb6 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -834,6 +834,10 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char
*slotname,
break;
}
}
+ else
+ {
+ appendStringInfoString(&cmd, " PHYSICAL RESERVE_WAL");
+ }
res = libpqrcv_PQexec(conn->streamConn, cmd.data);
pfree(cmd.data);
diff --git a/src/backend/replication/walreceiver.c
b/src/backend/replication/walreceiver.c
index 77360f1524..b464114333 100644
--- a/src/backend/replication/walreceiver.c
+++ b/src/backend/replication/walreceiver.c
@@ -73,6 +73,7 @@
/* GUC variables */
+bool wal_receiver_create_temp_slot;
int wal_receiver_status_interval;
int wal_receiver_timeout;
bool hot_standby_feedback;
@@ -169,6 +170,7 @@ WalReceiverMain(void)
char conninfo[MAXCONNINFO];
char *tmp_conninfo;
char slotname[NAMEDATALEN];
+ bool is_temp_slot;
XLogRecPtr startpoint;
TimeLineID startpointTLI;
TimeLineID primaryTLI;
@@ -230,6 +232,7 @@ WalReceiverMain(void)
walrcv->ready_to_display = false;
strlcpy(conninfo, (char *) walrcv->conninfo, MAXCONNINFO);
strlcpy(slotname, (char *) walrcv->slotname, NAMEDATALEN);
+ is_temp_slot = walrcv->is_temp_slot;
startpoint = walrcv->receiveStart;
startpointTLI = walrcv->receiveStartTLI;
@@ -345,6 +348,44 @@ WalReceiverMain(void)
*/
WalRcvFetchTimeLineHistoryFiles(startpointTLI, primaryTLI);
+ /*
+ * Create temporary replication slot if no slot name is
configured or
+ * the slot from the previous run was temporary, unless
+ * wal_receiver_create_temp_slot is disabled. We also need to
handle
+ * the case where the previous run used a temporary slot but
+ * wal_receiver_create_temp_slot was changed in the meantime.
In that
+ * case, we delete the old slot name in shared memory. (This
would
+ * all be a bit easier if we just didn't copy the slot name into
+ * shared memory, since we won't need it again later, but then
we
+ * can't see the slot name in the stats views.)
+ */
+ if (slotname[0] == '\0' || is_temp_slot)
+ {
+ bool changed = false;
+
+ if (wal_receiver_create_temp_slot)
+ {
+ snprintf(slotname, sizeof(slotname),
+ "pg_walreceiver_%d",
walrcv_get_backend_pid(wrconn));
+
+ walrcv_create_slot(wrconn, slotname, true, 0,
NULL);
+ changed = true;
+ }
+ else if (slotname[0] != '\0')
+ {
+ slotname[0] = '\0';
+ changed = true;
+ }
+
+ if (changed)
+ {
+ SpinLockAcquire(&walrcv->mutex);
+ strlcpy(walrcv->slotname, slotname,
NAMEDATALEN);
+ walrcv->is_temp_slot =
wal_receiver_create_temp_slot;
+ SpinLockRelease(&walrcv->mutex);
+ }
+ }
+
/*
* Start streaming.
*
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 62285792ec..e5f8a1301f 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -1969,6 +1969,15 @@ static struct config_bool ConfigureNamesBool[] =
NULL, NULL, NULL
},
+ {
+ {"wal_receiver_create_temp_slot", PGC_SIGHUP,
REPLICATION_STANDBY,
+ gettext_noop("Sets whether a WAL receiver should create
a temporary replication slot if no permanent slot is configured."),
+ },
+ &wal_receiver_create_temp_slot,
+ true,
+ NULL, NULL, NULL
+ },
+
/* End-of-list marker */
{
{NULL, 0, 0, NULL, NULL}, NULL, false, NULL, NULL, NULL
diff --git a/src/backend/utils/misc/postgresql.conf.sample
b/src/backend/utils/misc/postgresql.conf.sample
index 087190ce63..e1048c0047 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -321,6 +321,7 @@
#max_standby_streaming_delay = 30s # max delay before canceling queries
# when reading streaming WAL;
# -1 allows indefinite delay
+#wal_receiver_create_temp_slot = on # create temp slot if primary_slot_name
not set
#wal_receiver_status_interval = 10s # send replies at least this often
# 0 disables
#hot_standby_feedback = off # send info from standby to prevent
diff --git a/src/include/replication/walreceiver.h
b/src/include/replication/walreceiver.h
index 172cfa2862..e08afc6548 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -23,6 +23,7 @@
#include "utils/tuplestore.h"
/* user-settable parameters */
+extern bool wal_receiver_create_temp_slot;
extern int wal_receiver_status_interval;
extern int wal_receiver_timeout;
extern bool hot_standby_feedback;
@@ -121,6 +122,12 @@ typedef struct
*/
char slotname[NAMEDATALEN];
+ /*
+ * If it's a temporary replication slot, it needs to be recreated when
+ * connecting.
+ */
+ bool is_temp_slot;
+
/* set true once conninfo is ready to display (obfuscated pwds etc) */
bool ready_to_display;
--
2.24.1
