Add a new DestReceiver for printing tuples without catalog access.

If you create a DestReciver of type DestRemote and try to use it from
a replication connection that is not bound to a specific daabase, or
any other hypothetical type of backend that is not bound to a specific
database, it will fail because it doesn't have a pg_proc catalog to
look up properties of the types being printed.  In general, that's
an unavoidable problem, but we can hardwire the properties of a few
builtin types in order to support utility commands.  This new
DestReceiver of type DestRemoteSimple does just that.

Patch by me, reviewed by Michael Paquier.

Discussion: http://postgr.es/m/CA+TgmobNo4qz06wHEmy9DszAre3dYx-WNhHSCbU9SAwf+9Ft6g@mail.gmail.com

diff --git a/src/backend/access/common/Makefile b/src/backend/access/common/Makefile
index 1fa6de0823a5e8cf3d71052499452f53a1821d2d..d4b8132a9739f430f1acb18934383cd64a68fb1d 100644 (file)
--- a/src/backend/access/common/Makefile
+++ b/src/backend/access/common/Makefile
@@ -12,7 +12,7 @@ subdir = src/backend/access/common
 top_builddir = ../../../..
 include $(top_builddir)/src/Makefile.global
 
-OBJS = heaptuple.o indextuple.o printtup.o reloptions.o scankey.o \
-   tupconvert.o tupdesc.o
+OBJS = heaptuple.o indextuple.o printsimple.o printtup.o reloptions.o \
+   scankey.o tupconvert.o tupdesc.o
 
 include $(top_srcdir)/src/backend/common.mk

diff --git a/src/backend/access/common/printsimple.c b/src/backend/access/common/printsimple.c
new file mode 100644 (file)
index 0000000..420de65
--- /dev/null
+++ b/src/backend/access/common/printsimple.c
@@ -0,0 +1,110 @@
+/*-------------------------------------------------------------------------
+ *
+ * printsimple.c
+ *   Routines to print out tuples containing only a limited range of
+ *   builtin types without catalog access.  This is intended for
+ *   backends that don't have catalog access because they are not bound
+ *   to a specific database, such as some walsender processes.  It
+ *   doesn't handle standalone backends or protocol versions other than
+ *   3.0, because we don't need such handling for current applications.
+ *
+ * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *   src/backend/access/common/printsimple.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "access/printsimple.h"
+#include "catalog/pg_type.h"
+#include "fmgr.h"
+#include "libpq/pqformat.h"
+
+/*
+ * At startup time, send a RowDescription message.
+ */
+void
+printsimple_startup(DestReceiver *self, int operation, TupleDesc tupdesc)
+{
+   StringInfoData buf;
+   int         i;
+
+   pq_beginmessage(&buf, 'T'); /* RowDescription */
+   pq_sendint(&buf, tupdesc->natts, 2);
+
+   for (i = 0; i < tupdesc->natts; ++i)
+   {
+       Form_pg_attribute attr = tupdesc->attrs[i];
+
+       pq_sendstring(&buf, NameStr(attr->attname));
+       pq_sendint(&buf, 0, 4); /* table oid */
+       pq_sendint(&buf, 0, 2); /* attnum */
+       pq_sendint(&buf, (int) attr->atttypid, 4);
+       pq_sendint(&buf, attr->attlen, 2);
+       pq_sendint(&buf, attr->atttypmod, 4);
+       pq_sendint(&buf, 0, 2); /* format code */
+   }
+
+   pq_endmessage(&buf);
+}
+
+/*
+ * For each tuple, send a DataRow message.
+ */
+bool
+printsimple(TupleTableSlot *slot, DestReceiver *self)
+{
+   TupleDesc   tupdesc = slot->tts_tupleDescriptor;
+   StringInfoData buf;
+   int         i;
+
+   /* Make sure the tuple is fully deconstructed */
+   slot_getallattrs(slot);
+
+   /* Prepare and send message */
+   pq_beginmessage(&buf, 'D');
+   pq_sendint(&buf, tupdesc->natts, 2);
+
+   for (i = 0; i < tupdesc->natts; ++i)
+   {
+       Form_pg_attribute attr = tupdesc->attrs[i];
+       Datum       value;
+
+       if (slot->tts_isnull[i])
+       {
+           pq_sendint(&buf, -1, 4);
+           continue;
+       }
+
+       value = slot->tts_values[i];
+
+       /*
+        * We can't call the regular type output functions here because we
+        * might not have catalog access.  Instead, we must hard-wire
+        * knowledge of the required types.
+        */
+       switch (attr->atttypid)
+       {
+           case TEXTOID:
+               {
+                   text       *t = DatumGetTextPP(value);
+
+                   pq_sendcountedtext(&buf,
+                                      VARDATA_ANY(t),
+                                      VARSIZE_ANY_EXHDR(t),
+                                      false);
+               }
+               break;
+
+           default:
+               elog(ERROR, "unsupported type OID: %u", attr->atttypid);
+       }
+   }
+
+   pq_endmessage(&buf);
+
+   return true;
+}

diff --git a/src/backend/tcop/dest.c b/src/backend/tcop/dest.c
index da39f43f38c3e7be68d5732faf32486ae7cbb7b0..28081c37654a8787e9423e75c6f768997d6872ca 100644 (file)
--- a/src/backend/tcop/dest.c
+++ b/src/backend/tcop/dest.c
@@ -28,6 +28,7 @@
 
 #include "postgres.h"
 
+#include "access/printsimple.h"
 #include "access/printtup.h"
 #include "access/xact.h"
 #include "commands/copy.h"
@@ -76,6 +77,11 @@ static DestReceiver debugtupDR = {
    DestDebug
 };
 
+static DestReceiver printsimpleDR = {
+   printsimple, printsimple_startup, donothingCleanup, donothingCleanup,
+   DestRemoteSimple
+};
+
 static DestReceiver spi_printtupDR = {
    spi_printtup, spi_dest_startup, donothingCleanup, donothingCleanup,
    DestSPI
@@ -108,6 +114,9 @@ CreateDestReceiver(CommandDest dest)
        case DestRemoteExecute:
            return printtup_create_DR(dest);
 
+       case DestRemoteSimple:
+           return &printsimpleDR;
+
        case DestNone:
            return &donothingDR;
 
@@ -151,6 +160,7 @@ EndCommand(const char *commandTag, CommandDest dest)
    {
        case DestRemote:
        case DestRemoteExecute:
+       case DestRemoteSimple:
 
            /*
             * We assume the commandTag is plain ASCII and therefore requires
@@ -191,6 +201,7 @@ NullCommand(CommandDest dest)
    {
        case DestRemote:
        case DestRemoteExecute:
+       case DestRemoteSimple:
 
            /*
             * tell the fe that we saw an empty query string.  In protocols
@@ -233,6 +244,7 @@ ReadyForQuery(CommandDest dest)
    {
        case DestRemote:
        case DestRemoteExecute:
+       case DestRemoteSimple:
            if (PG_PROTOCOL_MAJOR(FrontendProtocol) >= 3)
            {
                StringInfoData buf;

diff --git a/src/include/access/printsimple.h b/src/include/access/printsimple.h
new file mode 100644 (file)
index 0000000..3f3e7a3
--- /dev/null
+++ b/src/include/access/printsimple.h
@@ -0,0 +1,23 @@
+/*-------------------------------------------------------------------------
+ *
+ * printsimple.h
+ *   print simple tuples without catalog access
+ *
+ * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/access/printsimple.h
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#ifndef PRINTSIMPLE_H
+#define PRINTSIMPLE_H
+
+#include "tcop/dest.h"
+
+extern bool printsimple(TupleTableSlot *slot, DestReceiver *self);
+extern void printsimple_startup(DestReceiver *self, int operation,
+                   TupleDesc tupdesc);
+
+#endif   /* PRINTSIMPLE_H */

diff --git a/src/include/tcop/dest.h b/src/include/tcop/dest.h
index 93f9b7463abe2dd8d06a98b19fc287e3b7155c79..c459af2e139ee598b7ee1cc6c64d7b3cf029025a 100644 (file)
--- a/src/include/tcop/dest.h
+++ b/src/include/tcop/dest.h
@@ -89,6 +89,7 @@ typedef enum
    DestDebug,                  /* results go to debugging output */
    DestRemote,                 /* results sent to frontend process */
    DestRemoteExecute,          /* sent to frontend, in Execute command */
+   DestRemoteSimple,           /* sent to frontend, w/no catalog access */
    DestSPI,                    /* results sent to SPI manager */
    DestTuplestore,             /* results sent to Tuplestore */
    DestIntoRel,                /* results sent to relation (SELECT INTO) */