Improve REPACK (CONCURRENTLY) error when wal_level < replica

The error emitted when REPACK (CONCURRENTLY) is run with too low a
wal_level is thrown by CheckSlotRequirements(), which is a bit
mysterious when the user doesn't know what's up.  Add an upfront check
in check_concurrent_repack_requirements() for a more explicit, REPACK-
centered report, which is easier to understand -- this also saves
starting the worker just to have it die immediately.

Author: Baji Shaik <baji.pgdev@gmail.com>
Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Discussion: https://postgr.es/m/CA+fm-ROdgh0rEVuXoViBk4TVgjodrN=MTR_RYuOuKLZ9voX4YA@mail.gmail.com

diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index da9d941f4a1a2452e2bcd69765bd1a7197ccc39d..c5d85eced483c0513c8762111df137121028fdf4 100644 (file)
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -40,6 +40,7 @@
 #include "access/toast_internals.h"
 #include "access/transam.h"
 #include "access/xact.h"
+#include "access/xlog.h"
 #include "catalog/catalog.h"
 #include "catalog/dependency.h"
 #include "catalog/heap.h"
@@ -897,6 +898,14 @@ check_concurrent_repack_requirements(Relation rel, Oid *ident_idx_p)
                                replident;
        Oid                     ident_idx;
 
+       if (wal_level < WAL_LEVEL_REPLICA)
+               ereport(ERROR,
+                               errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+                               errmsg("cannot execute \"%s\" in this configuration",
+                                          "REPACK (CONCURRENTLY)"),
+                               errdetail("%s requires \"wal_level\" to be set to \"replica\" or higher.",
+                                                 "REPACK (CONCURRENTLY)"));
+
        /* Data changes in system relations are not logically decoded. */
        if (IsCatalogRelation(rel))
                ereport(ERROR,