Optionally disable subscriptions on error.

Logical replication apply workers for a subscription can easily get stuck
in an infinite loop of attempting to apply a change, triggering an error
(such as a constraint violation), exiting with the error written to the
subscription server log, and restarting.

To partially remedy the situation, this patch adds a new subscription
option named 'disable_on_error'. To be consistent with old behavior, this
option defaults to false. When true, both the tablesync worker and apply
worker catch any errors thrown and disable the subscription in order to
break the loop. The error is still also written in the logs.

Once the subscription is disabled, users can either manually resolve the
conflict/error or skip the conflicting transaction by using
pg_replication_origin_advance() function. After resolving the conflict,
users need to enable the subscription to allow apply process to proceed.

Author: Osumi Takamichi and Mark Dilger
Reviewed-by: Greg Nancarrow, Vignesh C, Amit Kapila, Wang wei, Tang Haiying, Peter Smith, Masahiko Sawada, Shi Yu
Discussion : https://postgr.es/m/DB35438F-9356-4841-89A0-412709EBD3AB%40enterprisedb.com

Author: Amit Kapila

doc/src/sgml/catalogs.sgml

@@ -7769,6 +7769,16 @@ SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</replaceable>:<replaceable>&l
       </para></entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>subdisableonerr</structfield> <type>bool</type>
+      </para>
+      <para>
+       If true, the subscription will be disabled if one of its workers
+       detects an error
+      </para></entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>subconninfo</structfield> <type>text</type>

doc/src/sgml/logical-replication.sgml

@@ -364,8 +364,9 @@ CONTEXT:  processing remote data for replication origin "pg_16395" during "INSER
    the replication origin name can be found from the server log (LSN 0/14C0378 and
    replication origin <literal>pg_16395</literal> in the above case).  To skip the
    transaction, the subscription needs to be disabled temporarily by
-   <command>ALTER SUBSCRIPTION ... DISABLE</command> first. Then, the transaction
-   can be skipped by calling the
+   <command>ALTER SUBSCRIPTION ... DISABLE</command> first or alternatively, the
+   subscription can be used with the <literal>disable_on_error</literal> option.
+   Then, the transaction can be skipped by calling the
    <link linkend="pg-replication-origin-advance">
    <function>pg_replication_origin_advance()</function></link> function with
    the <parameter>node_name</parameter> (i.e., <literal>pg_16395</literal>) and the

doc/src/sgml/ref/alter_subscription.sgml

@@ -204,8 +204,8 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       information.  The parameters that can be altered
       are <literal>slot_name</literal>,
       <literal>synchronous_commit</literal>,
-      <literal>binary</literal>, and
-      <literal>streaming</literal>.
+      <literal>binary</literal>, <literal>streaming</literal>, and
+      <literal>disable_on_error</literal>.
      </para>
     </listitem>
    </varlistentry>

doc/src/sgml/ref/create_subscription.sgml

@@ -290,6 +290,18 @@ CREATE SUBSCRIPTION <replaceable class="parameter">subscription_name</replaceabl
 
         </listitem>
        </varlistentry>
+
+       <varlistentry>
+        <term><literal>disable_on_error</literal> (<type>boolean</type>)</term>
+        <listitem>
+         <para>
+          Specifies whether the subscription should be automatically disabled
+          if any errors are detected by subscription workers during data
+          replication from the publisher. The default is
+          <literal>false</literal>.
+         </para>
+        </listitem>
+       </varlistentry>
       </variablelist>
      </para>
 

src/backend/catalog/pg_subscription.c

@@ -69,6 +69,7 @@ GetSubscription(Oid subid, bool missing_ok)
 	sub->binary = subform->subbinary;
 	sub->stream = subform->substream;
 	sub->twophasestate = subform->subtwophasestate;
+	sub->disableonerr = subform->subdisableonerr;
 
 	/* Get conninfo */
 	datum = SysCacheGetAttr(SUBSCRIPTIONOID,
@@ -156,6 +157,45 @@ FreeSubscription(Subscription *sub)
 	pfree(sub);
 }
 
+/*
+ * Disable the given subscription.
+ */
+void
+DisableSubscription(Oid subid)
+{
+	Relation	rel;
+	bool		nulls[Natts_pg_subscription];
+	bool		replaces[Natts_pg_subscription];
+	Datum		values[Natts_pg_subscription];
+	HeapTuple	tup;
+
+	/* Look up the subscription in the catalog */
+	rel = table_open(SubscriptionRelationId, RowExclusiveLock);
+	tup = SearchSysCacheCopy1(SUBSCRIPTIONOID, ObjectIdGetDatum(subid));
+
+	if (!HeapTupleIsValid(tup))
+		elog(ERROR, "cache lookup failed for subscription %u", subid);
+
+	LockSharedObject(SubscriptionRelationId, subid, 0, AccessShareLock);
+
+	/* Form a new tuple. */
+	memset(values, 0, sizeof(values));
+	memset(nulls, false, sizeof(nulls));
+	memset(replaces, false, sizeof(replaces));
+
+	/* Set the subscription to disabled. */
+	values[Anum_pg_subscription_subenabled - 1] = BoolGetDatum(false);
+	replaces[Anum_pg_subscription_subenabled - 1] = true;
+
+	/* Update the catalog */
+	tup = heap_modify_tuple(tup, RelationGetDescr(rel), values, nulls,
+							replaces);
+	CatalogTupleUpdate(rel, &tup->t_self, tup);
+	heap_freetuple(tup);
+
+	table_close(rel, NoLock);
+}
+
 /*
  * get_subscription_oid - given a subscription name, look up the OID
  *

src/backend/catalog/system_views.sql

@@ -1261,7 +1261,8 @@ REVOKE ALL ON pg_replication_origin_status FROM public;
 -- All columns of pg_subscription except subconninfo are publicly readable.
 REVOKE ALL ON pg_subscription FROM public;
 GRANT SELECT (oid, subdbid, subname, subowner, subenabled, subbinary,
-              substream, subtwophasestate, subslotname, subsynccommit, subpublications)
+              substream, subtwophasestate, subdisableonerr, subslotname,
+              subsynccommit, subpublications)
     ON pg_subscription TO public;
 
 CREATE VIEW pg_stat_subscription_stats AS

src/backend/commands/subscriptioncmds.c

@@ -61,6 +61,7 @@
 #define SUBOPT_BINARY				0x00000080
 #define SUBOPT_STREAMING			0x00000100
 #define SUBOPT_TWOPHASE_COMMIT		0x00000200
+#define SUBOPT_DISABLE_ON_ERR		0x00000400
 
 /* check if the 'val' has 'bits' set */
 #define IsSet(val, bits)  (((val) & (bits)) == (bits))
@@ -82,6 +83,7 @@ typedef struct SubOpts
 	bool		binary;
 	bool		streaming;
 	bool		twophase;
+	bool		disableonerr;
 } SubOpts;
 
 static List *fetch_table_list(WalReceiverConn *wrconn, List *publications);
@@ -130,6 +132,8 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 		opts->streaming = false;
 	if (IsSet(supported_opts, SUBOPT_TWOPHASE_COMMIT))
 		opts->twophase = false;
+	if (IsSet(supported_opts, SUBOPT_DISABLE_ON_ERR))
+		opts->disableonerr = false;
 
 	/* Parse options */
 	foreach(lc, stmt_options)
@@ -249,6 +253,15 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 			opts->specified_opts |= SUBOPT_TWOPHASE_COMMIT;
 			opts->twophase = defGetBoolean(defel);
 		}
+		else if (IsSet(supported_opts, SUBOPT_DISABLE_ON_ERR) &&
+				 strcmp(defel->defname, "disable_on_error") == 0)
+		{
+			if (IsSet(opts->specified_opts, SUBOPT_DISABLE_ON_ERR))
+				errorConflictingDefElem(defel, pstate);
+
+			opts->specified_opts |= SUBOPT_DISABLE_ON_ERR;
+			opts->disableonerr = defGetBoolean(defel);
+		}
 		else
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
@@ -390,7 +403,8 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 	supported_opts = (SUBOPT_CONNECT | SUBOPT_ENABLED | SUBOPT_CREATE_SLOT |
 					  SUBOPT_SLOT_NAME | SUBOPT_COPY_DATA |
 					  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
-					  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT);
+					  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
+					  SUBOPT_DISABLE_ON_ERR);
 	parse_subscription_options(pstate, stmt->options, supported_opts, &opts);
 
 	/*
@@ -464,6 +478,7 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 		CharGetDatum(opts.twophase ?
 					 LOGICALREP_TWOPHASE_STATE_PENDING :
 					 LOGICALREP_TWOPHASE_STATE_DISABLED);
+	values[Anum_pg_subscription_subdisableonerr - 1] = BoolGetDatum(opts.disableonerr);
 	values[Anum_pg_subscription_subconninfo - 1] =
 		CStringGetTextDatum(conninfo);
 	if (opts.slot_name)
@@ -864,7 +879,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 			{
 				supported_opts = (SUBOPT_SLOT_NAME |
 								  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
-								  SUBOPT_STREAMING);
+								  SUBOPT_STREAMING | SUBOPT_DISABLE_ON_ERR);
 
 				parse_subscription_options(pstate, stmt->options,
 										   supported_opts, &opts);
@@ -913,6 +928,14 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					replaces[Anum_pg_subscription_substream - 1] = true;
 				}
 
+				if (IsSet(opts.specified_opts, SUBOPT_DISABLE_ON_ERR))
+				{
+					values[Anum_pg_subscription_subdisableonerr - 1]
+						= BoolGetDatum(opts.disableonerr);
+					replaces[Anum_pg_subscription_subdisableonerr - 1]
+						= true;
+				}
+
 				update_tuple = true;
 				break;
 			}