Don't build full initial logical decoding snapshot if NOEXPORT_SNAPSHOT.

Earlier commits (56e19d938dd14 and 2bef06d5164) make it cheaper to
create a logical slot if not exporting the initial snapshot.  If
NOEXPORT_SNAPSHOT is specified, we can skip the overhead, not just
when creating a slot via sql (which can't export snapshots).  As
NOEXPORT_SNAPSHOT has only recently been introduced, this shouldn't be
backpatched.

diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 43c8a73f3e1f763472fce2f36efd197e30a47669..2a6c8bb62dfba479ddfd908f20f4887de956a53d 100644 (file)
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -873,6 +873,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
    if (cmd->kind == REPLICATION_KIND_LOGICAL)
    {
        LogicalDecodingContext *ctx;
+       bool    need_full_snapshot = false;
 
        /*
         * Do options check early so that we can bail before calling the
@@ -884,6 +885,8 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
                ereport(ERROR,
                        (errmsg("CREATE_REPLICATION_SLOT ... EXPORT_SNAPSHOT "
                                "must not be called inside a transaction")));
+
+           need_full_snapshot = true;
        }
        else if (snapshot_action == CRS_USE_SNAPSHOT)
        {
@@ -906,10 +909,11 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
                ereport(ERROR,
                        (errmsg("CREATE_REPLICATION_SLOT ... USE_SNAPSHOT "
                                "must not be called in a subtransaction")));
+
+           need_full_snapshot = true;
        }
 
-       ctx = CreateInitDecodingContext(cmd->plugin, NIL,
-                                       true, /* build snapshot */
+       ctx = CreateInitDecodingContext(cmd->plugin, NIL, need_full_snapshot,
                                        logical_read_xlog_page,
                                        WalSndPrepareWrite, WalSndWriteData);