From: Alvaro Herrera <alvherre@alvh.no-ip.org>
Date: Tue, 27 Oct 2020 17:31:37 +0000 (-0300)
Subject: pg_dump: Lock all relations, not just plain tables
X-Git-Tag: REL9_5_24~17
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=d9ed510ef64bb1962b2084f5b43aad03f1bd5cfa;p=thirdparty%2Fpostgresql.git

pg_dump: Lock all relations, not just plain tables

Now that LOCK TABLE can take any relation type, acquire lock on all
relations that are to be dumped.  This prevents schema changes or
deadlock errors that could cause a dump to fail after expending much
effort.  The server is tested to have the capability and the feature
disabled if it doesn't, so that a patched pg_dump doesn't fail when
connecting to an unpatched server.

Backpatch to 9.5.

Author: Álvaro Herrera <alvherre@alvh.no-ip.org>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reported-by: Wells Oliver <wells.oliver@gmail.com>
Discussion: https://postgr.es/m/20201021200659.GA32358@alvherre.pgsql
---

diff --git a/src/bin/pg_dump/pg_backup.h b/src/bin/pg_dump/pg_backup.h
index 8ae1388be41..876a97b5087 100644
--- a/src/bin/pg_dump/pg_backup.h
+++ b/src/bin/pg_dump/pg_backup.h
@@ -187,6 +187,8 @@ typedef struct Archive
 	int			minRemoteVersion;		/* allowable range */
 	int			maxRemoteVersion;
 
+	bool		hasGenericLockTable;	/* can LOCK TABLE do non-table rels */
+
 	int			numWorkers;		/* number of parallel processes */
 	char	   *sync_snapshot_id;		/* sync snapshot id for parallel
 										 * operation */
diff --git a/src/bin/pg_dump/pg_backup_db.c b/src/bin/pg_dump/pg_backup_db.c
index 6559151f518..2fd6789ccea 100644
--- a/src/bin/pg_dump/pg_backup_db.c
+++ b/src/bin/pg_dump/pg_backup_db.c
@@ -551,6 +551,71 @@ EndDBCopyMode(Archive *AHX, const char *tocEntryTag)
 	}
 }
 
+/*
+ * Does LOCK TABLE work on non-table relations on this server?
+ *
+ * Note: assumes it is called out of any transaction
+ */
+bool
+IsLockTableGeneric(Archive *AHX)
+{
+	ArchiveHandle *AH = (ArchiveHandle *) AHX;
+	PGresult *res;
+	char	 *sqlstate;
+	bool	retval;
+
+	if (AHX->remoteVersion >= 140000)
+		return true;
+	else if (AHX->remoteVersion < 90500)
+		return false;
+
+	StartTransaction(AHX);
+
+	/*
+	 * Try a LOCK TABLE on a well-known non-table catalog; WRONG_OBJECT_TYPE
+	 * tells us that this server doesn't support locking non-table rels, while
+	 * LOCK_NOT_AVAILABLE and INSUFFICIENT_PRIVILEGE tell us that it does.
+	 * Report anything else as a fatal problem.
+	 */
+#define ERRCODE_INSUFFICIENT_PRIVILEGE	"42501"
+#define ERRCODE_WRONG_OBJECT_TYPE	"42809"
+#define ERRCODE_LOCK_NOT_AVAILABLE	"55P03"
+	res = PQexec(AH->connection,
+				 "LOCK TABLE pg_catalog.pg_class_tblspc_relfilenode_index IN ACCESS SHARE MODE NOWAIT");
+	switch (PQresultStatus(res))
+	{
+		case PGRES_COMMAND_OK:
+			retval = true;
+			break;
+		case PGRES_FATAL_ERROR:
+			sqlstate = PQresultErrorField(res, PG_DIAG_SQLSTATE);
+			if (strcmp(sqlstate, ERRCODE_WRONG_OBJECT_TYPE) == 0)
+			{
+				retval = false;
+				break;
+			}
+			else if (strcmp(sqlstate, ERRCODE_LOCK_NOT_AVAILABLE) == 0 ||
+					 strcmp(sqlstate, ERRCODE_INSUFFICIENT_PRIVILEGE) == 0)
+			{
+				retval = true;
+				break;
+			}
+			/* else, falls through */
+		default:
+			warn_or_exit_horribly(AH, modulename,
+								  "LOCK TABLE failed for \"%s\": %s",
+								  "pg_catalog.pg_class_tblspc_relfilenode_index",
+								  PQerrorMessage(AH->connection));
+			retval = false;		/* not reached */
+			break;
+	}
+	PQclear(res);
+
+	CommitTransaction(AHX);
+
+	return retval;
+}
+
 void
 StartTransaction(Archive *AHX)
 {
diff --git a/src/bin/pg_dump/pg_backup_db.h b/src/bin/pg_dump/pg_backup_db.h
index 527449e0440..9e7a84fdee9 100644
--- a/src/bin/pg_dump/pg_backup_db.h
+++ b/src/bin/pg_dump/pg_backup_db.h
@@ -20,6 +20,8 @@ extern PGresult *ExecuteSqlQueryForSingleRow(Archive *fout, char *query);
 
 extern void EndDBCopyMode(Archive *AHX, const char *tocEntryTag);
 
+extern bool IsLockTableGeneric(Archive *AHX);
+
 extern void StartTransaction(Archive *AHX);
 extern void CommitTransaction(Archive *AHX);
 
diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index b30b87ae66d..c886ffefbd0 100644
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -1062,6 +1062,9 @@ setup_connection(Archive *AH, const char *dumpencoding,
 			ExecuteSqlStatement(AH, "SET row_security = off");
 	}
 
+	/* Detect whether LOCK TABLE can handle non-table relations */
+	AH->hasGenericLockTable = IsLockTableGeneric(AH);
+
 	/*
 	 * Start transaction-snapshot mode transaction to dump consistent data.
 	 */
@@ -5398,10 +5401,12 @@ getTables(Archive *fout, int *numTables)
 		 * assume our lock on the child is enough to prevent schema
 		 * alterations to parent tables.
 		 *
-		 * NOTE: it'd be kinda nice to lock other relations too, not only
-		 * plain tables, but the backend doesn't presently allow that.
+		 * On server versions that support it, we lock all relations not just
+		 * plain tables.
 		 */
-		if (tblinfo[i].dobj.dump && tblinfo[i].relkind == RELKIND_RELATION)
+		if (tblinfo[i].dobj.dump &&
+			(fout->hasGenericLockTable ||
+			 tblinfo[i].relkind == RELKIND_RELATION))
 		{
 			resetPQExpBuffer(query);
 			appendPQExpBuffer(query,