pg_dump: Fix query for gathering attribute stats on older versions.

Commit 9c02e3a986 taught pg_dump to retrieve attribute statistics
for 64 relations at a time.  pg_dump supports dumping from v9.2 and
newer versions, but our query for retrieving statistics for
multiple relations uses WITH ORDINALITY and multi-argument
UNNEST(), both of which were introduced in v9.4.  To fix, we resort
to gathering statistics for a single relation at a time on versions
older than v9.4.

Per buildfarm member crake.

Author: Corey Huinker <corey.huinker@gmail.com>
Discussion: https://postgr.es/m/Z_BcWVMvlUIJ_iuZ%40nathan

diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index 0e915432e77a11b3af3a110cf80ee1bf2b70b7ad..8e6364d32d72cefaf5007e1c25daea27eb4b3403 100644 (file)
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -10571,6 +10571,16 @@ fetchAttributeStats(Archive *fout)
        PGresult   *res = NULL;
        static TocEntry *te;
        static bool restarted;
+       int                     max_rels = MAX_ATTR_STATS_RELS;
+
+       /*
+        * Our query for retrieving statistics for multiple relations uses WITH
+        * ORDINALITY and multi-argument UNNEST(), both of which were introduced
+        * in v9.4.  For older versions, we resort to gathering statistics for a
+        * single relation at a time.
+        */
+       if (fout->remoteVersion < 90400)
+               max_rels = 1;
 
        /* If we're just starting, set our TOC pointer. */
        if (!te)
@@ -10596,7 +10606,7 @@ fetchAttributeStats(Archive *fout)
         * This is perhaps not the sturdiest assumption, so we verify it matches
         * reality in dumpRelationStats_dumper().
         */
-       for (; te != AH->toc && count < MAX_ATTR_STATS_RELS; te = te->next)
+       for (; te != AH->toc && count < max_rels; te = te->next)
        {
                if ((te->reqs & REQ_STATS) != 0 &&
                        strcmp(te->desc, "STATISTICS DATA") == 0)
@@ -10709,14 +10719,26 @@ dumpRelationStats_dumper(Archive *fout, const void *userArg, const TocEntry *te)
                 * sufficient to convince the planner to use
                 * pg_class_relname_nsp_index, which avoids a full scan of pg_stats.
                 * This may not work for all versions.
+                *
+                * Our query for retrieving statistics for multiple relations uses
+                * WITH ORDINALITY and multi-argument UNNEST(), both of which were
+                * introduced in v9.4.  For older versions, we resort to gathering
+                * statistics for a single relation at a time.
                 */
-               appendPQExpBufferStr(query,
-                                                        "FROM pg_catalog.pg_stats s "
-                                                        "JOIN unnest($1, $2) WITH ORDINALITY AS u (schemaname, tablename, ord) "
-                                                        "ON s.schemaname = u.schemaname "
-                                                        "AND s.tablename = u.tablename "
-                                                        "WHERE s.tablename = ANY($2) "
-                                                        "ORDER BY u.ord, s.attname, s.inherited");
+               if (fout->remoteVersion >= 90400)
+                       appendPQExpBufferStr(query,
+                                                                "FROM pg_catalog.pg_stats s "
+                                                                "JOIN unnest($1, $2) WITH ORDINALITY AS u (schemaname, tablename, ord) "
+                                                                "ON s.schemaname = u.schemaname "
+                                                                "AND s.tablename = u.tablename "
+                                                                "WHERE s.tablename = ANY($2) "
+                                                                "ORDER BY u.ord, s.attname, s.inherited");
+               else
+                       appendPQExpBufferStr(query,
+                                                                "FROM pg_catalog.pg_stats s "
+                                                                "WHERE s.schemaname = $1[1] "
+                                                                "AND s.tablename = $2[1] "
+                                                                "ORDER BY s.attname, s.inherited");
 
                ExecuteSqlStatement(fout, query->data);