Create an infrastructure for parallel computation in PostgreSQL.

This does four basic things.  First, it provides convenience routines
to coordinate the startup and shutdown of parallel workers.  Second,
it synchronizes various pieces of state (e.g. GUCs, combo CID
mappings, transaction snapshot) from the parallel group leader to the
worker processes.  Third, it prohibits various operations that would
result in unsafe changes to that state while parallelism is active.
Finally, it propagates events that would result in an ErrorResponse,
NoticeResponse, or NotifyResponse message being sent to the client
from the parallel workers back to the master, from which they can then
be sent on to the client.

Robert Haas, Amit Kapila, Noah Misch, Rushabh Lathia, Jeevan Chalke.
Suggestions and review from Andres Freund, Heikki Linnakangas, Noah
Misch, Simon Riggs, Euler Taveira, and Jim Nasby.

2 files changed, 16 insertions, 1 deletions

diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c
index 92ff632e124..0d3721a96da 100644
--- a/src/backend/commands/copy.c
+++ b/src/backend/commands/copy.c
@@ -924,9 +924,10 @@ DoCopy(const CopyStmt *stmt, const char *queryString, uint64 *processed)
 	{
 		Assert(rel);
 
-		/* check read-only transaction */
+		/* check read-only transaction and parallel mode */
 		if (XactReadOnly && !rel->rd_islocaltemp)
 			PreventCommandIfReadOnly("COPY FROM");
+		PreventCommandIfParallelMode("COPY FROM");
 
 		cstate = BeginCopyFrom(rel, stmt->filename, stmt->is_program,
 							   stmt->attlist, stmt->options);
diff --git a/src/backend/commands/sequence.c b/src/backend/commands/sequence.c
index 6d316d62b6c..80f5553d3a4 100644
--- a/src/backend/commands/sequence.c
+++ b/src/backend/commands/sequence.c
@@ -565,6 +565,13 @@ nextval_internal(Oid relid)
 	if (!seqrel->rd_islocaltemp)
 		PreventCommandIfReadOnly("nextval()");
 
+	/*
+	 * Forbid this during parallel operation because, to make it work,
+	 * the cooperating backends would need to share the backend-local cached
+	 * sequence information.  Currently, we don't support that.
+	 */
+	PreventCommandIfParallelMode("nextval()");
+
 	if (elm->last != elm->cached)		/* some numbers were cached */
 	{
 		Assert(elm->last_valid);
@@ -862,6 +869,13 @@ do_setval(Oid relid, int64 next, bool iscalled)
 	if (!seqrel->rd_islocaltemp)
 		PreventCommandIfReadOnly("setval()");
 
+	/*
+	 * Forbid this during parallel operation because, to make it work,
+	 * the cooperating backends would need to share the backend-local cached
+	 * sequence information.  Currently, we don't support that.
+	 */
+	PreventCommandIfParallelMode("setval()");
+
 	/* lock page' buffer and read tuple */
 	seq = read_seq_tuple(elm, seqrel, &buf, &seqtuple);