Disable parallel query by default.

Per discussion, set the default value of max_parallel_workers_per_gather
to 0 in 9.6 only.  We'll leave it enabled in master so that it gets
more testing and in the hope that it can be enable by default in v10.

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 02f917b375ec82501474465f615b3882d50621c4..27176aa07c40c7764e34cb3520b95f25c0c48a10 100644 (file)
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -2008,7 +2008,7 @@ include_dir 'conf.d'
          <xref linkend="guc-max-worker-processes">.  Note that the requested
          number of workers may not actually be available at run time.  If this
          occurs, the plan will run with fewer workers than expected, which may
-         be inefficient.  The default value is 2.  Setting this value to 0
+         be inefficient.  Setting this value to 0, which is the default,
          disables parallel query execution.
         </para>
 

diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c
index 2a49639f1254a1e564169ff0cb4587a79b40f823..4ad1782bbf7048421d1d4e9957cb1ecf730de9ee 100644 (file)
--- a/src/backend/optimizer/path/costsize.c
+++ b/src/backend/optimizer/path/costsize.c
@@ -113,7 +113,7 @@ int                 effective_cache_size = DEFAULT_EFFECTIVE_CACHE_SIZE;
 
 Cost           disable_cost = 1.0e10;
 
-int                    max_parallel_workers_per_gather = 2;
+int                    max_parallel_workers_per_gather = 0;
 
 bool           enable_seqscan = true;
 bool           enable_indexscan = true;

diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 9c93df0f0a49efbecee3e7dc8cc60dd73cd9af46..0a58ba1faeb0b6f3694c023e7e88829241549f3d 100644 (file)
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -2652,7 +2652,7 @@ static struct config_int ConfigureNamesInt[] =
                        NULL
                },
                &max_parallel_workers_per_gather,
-               2, 0, 1024,
+               0, 0, 1024,
                NULL, NULL, NULL
        },
 

diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 6d0666c44fc865a9a7e85d5dc76500dcc1bbf9de..9644a667ff87a8172a984ea0d77fa23661f03805 100644 (file)
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -163,7 +163,7 @@
 
 #effective_io_concurrency = 1          # 1-1000; 0 disables prefetching
 #max_worker_processes = 8              # (change requires restart)
-#max_parallel_workers_per_gather = 2   # taken from max_worker_processes
+#max_parallel_workers_per_gather = 0   # taken from max_worker_processes
 #old_snapshot_threshold = -1           # 1min-60d; -1 disables; 0 is immediate
                                                                        # (change requires restart)
 #backend_flush_after = 0               # 0 disables, default is 0