Limit maximum parallel degree to 1024.

This new limit affects both the max_parallel_degree GUC and the
parallel_degree reloption.  There may some day be a use case for using
more than 1024 CPUs for a single query, but that's surely not the case
right now.  Not only do not very many people have that many CPUs, but
the code hasn't been tested at that kind of scale and is very unlikely
to perform well, or even work at all, without a lot more work.  The
issue addressed by commit 06bd458cb812623c3f1fdd55216c4c08b06a8447 is
probably just one problem of many.

The idea of a more reasonable limit here was suggested by Tom Lane;
the value of 1024 was suggested by Amit Kapila.

diff --git a/src/backend/access/common/reloptions.c b/src/backend/access/common/reloptions.c
index 797be63c44b34d0a7f757c1c2ecdcd1772f57f5e..7448c7f30fe4d530213e4a079ee2a75f22d05ad6 100644 (file)
--- a/src/backend/access/common/reloptions.c
+++ b/src/backend/access/common/reloptions.c
@@ -275,7 +275,7 @@ static relopt_int intRelOpts[] =
                        RELOPT_KIND_HEAP,
                        AccessExclusiveLock
                },
-               -1, 0, MAX_BACKENDS
+               -1, 0, 1024
        },
 
        /* list terminator */

diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 752f823a164f2cc968c17b1ff15ce301e6a2c920..e246a9c2f0b8e78d25a2a6e17c6b530b019630fc 100644 (file)
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -2662,7 +2662,7 @@ static struct config_int ConfigureNamesInt[] =
                        NULL
                },
                &max_parallel_degree,
-               2, 0, MAX_BACKENDS,
+               2, 0, 1024,
                NULL, NULL, NULL
        },