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 cbd7541577d215182412ccf5cee495bdd5fae792..4f0844255720d59819f4ea2f042b80438b21d9d8 100644 (file)
--- a/src/bin/pg_dump/pg_backup.h
+++ b/src/bin/pg_dump/pg_backup.h
@@ -188,6 +188,8 @@ 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 944d68a53c8d8f581e0eddf4c1332005df564ebb..3680ffabed76166ea303918bf6f4f76d4ad632e6 100644 (file)
--- a/src/bin/pg_dump/pg_backup_db.c
+++ b/src/bin/pg_dump/pg_backup_db.c
@@ -552,6 +552,71 @@ 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 527449e04401314006c00631d81b377663cf1e08..9e7a84fdee907eb91181d2260473037018825467 100644 (file)
--- 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 cda9f490a288e8f0897df0e2a89ea778165928fd..b2b3a0fc817c1e344549600998ed71e9c7f8971c 100644 (file)
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -1081,6 +1081,9 @@ 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.
     */
@@ -6197,13 +6200,15 @@ 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.
-        *
-        * We only need to lock the table for certain components; see
+        * We only need to lock the relation for certain components; see
         * pg_dump.h
+        *
+        * 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) &&
            (tblinfo[i].dobj.dump & DUMP_COMPONENTS_REQUIRING_LOCK))
        {
            resetPQExpBuffer(query);