Add a SHOW command to the replication command language.

This is useful infrastructure for an upcoming proposed patch to
allow the WAL segment size to be changed at initdb time; tools like
pg_basebackup need the ability to interrogate the server setting.
But it also doesn't seem like a bad thing to have independently of
that; it may find other uses in the future.

Robert Haas and Beena Emerson.  (The original patch here was by
Beena, but I rewrote it to such a degree that most of the code
being committed here is mine.)

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

diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index 5f89db5857021d6dba0dcf460f2d850a96ed9813..028ef10d91bd5b8274d2d610927f3835d94c45f5 100644 (file)
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -1393,6 +1393,30 @@ The commands accepted in walsender mode are:
     </listitem>
   </varlistentry>
 
+  <varlistentry>
+    <term><literal>SHOW</literal> <replaceable class="parameter">name</replaceable>
+     <indexterm><primary>SHOW</primary></indexterm>
+    </term>
+    <listitem>
+     <para>
+      Requests the server to send the current setting of a run-time parameter.
+      This is similar to the SQL command <xref linkend="sql-show">.
+     </para>
+
+     <variablelist>
+      <varlistentry>
+       <term><replaceable class="parameter">name</></term>
+       <listitem>
+         <para>
+          The name of a run-time parameter. Available parameters are documented
+          in <xref linkend="runtime-config">.
+         </para>
+       </listitem>
+      </varlistentry>
+     </variablelist>
+    </listitem>
+  </varlistentry>
+
   <varlistentry>
     <term><literal>TIMELINE_HISTORY</literal> <replaceable class="parameter">tli</replaceable>
      <indexterm><primary>TIMELINE_HISTORY</primary></indexterm>

diff --git a/src/backend/access/common/tupdesc.c b/src/backend/access/common/tupdesc.c
index 54a32c022349dc45836aef1fcc80b35f20f9c56c..083c0303dcfd0cd020862d6bf2d849d2e11633c9 100644 (file)
--- a/src/backend/access/common/tupdesc.c
+++ b/src/backend/access/common/tupdesc.c
@@ -20,6 +20,7 @@
 #include "postgres.h"
 
 #include "access/htup_details.h"
+#include "catalog/pg_collation.h"
 #include "catalog/pg_type.h"
 #include "miscadmin.h"
 #include "parser/parse_type.h"
@@ -553,6 +554,84 @@ TupleDescInitEntry(TupleDesc desc,
        ReleaseSysCache(tuple);
 }
 
+/*
+ * TupleDescInitBuiltinEntry
+ *             Initialize a tuple descriptor without catalog access.  Only
+ *             a limited range of builtin types are supported.
+ */
+void
+TupleDescInitBuiltinEntry(TupleDesc desc,
+                                                 AttrNumber attributeNumber,
+                                                 const char *attributeName,
+                                                 Oid oidtypeid,
+                                                 int32 typmod,
+                                                 int attdim)
+{
+       Form_pg_attribute att;
+
+       /* sanity checks */
+       AssertArg(PointerIsValid(desc));
+       AssertArg(attributeNumber >= 1);
+       AssertArg(attributeNumber <= desc->natts);
+
+       /* initialize the attribute fields */
+       att = desc->attrs[attributeNumber - 1];
+       att->attrelid = 0;                      /* dummy value */
+
+       /* unlike TupleDescInitEntry, we require an attribute name */
+       Assert(attributeName != NULL);
+       namestrcpy(&(att->attname), attributeName);
+
+       att->attstattarget = -1;
+       att->attcacheoff = -1;
+       att->atttypmod = typmod;
+
+       att->attnum = attributeNumber;
+       att->attndims = attdim;
+
+       att->attnotnull = false;
+       att->atthasdef = false;
+       att->attisdropped = false;
+       att->attislocal = true;
+       att->attinhcount = 0;
+       /* attacl, attoptions and attfdwoptions are not present in tupledescs */
+
+       att->atttypid = oidtypeid;
+
+       /*
+        * Our goal here is to support just enough types to let basic builtin
+        * commands work without catalog access - e.g. so that we can do certain
+        * things even in processes that are not connected to a database.
+        */
+       switch (oidtypeid)
+       {
+               case TEXTOID:
+               case TEXTARRAYOID:
+                       att->attlen = -1;
+                       att->attbyval = false;
+                       att->attalign = 'i';
+                       att->attstorage = 'x';
+                       att->attcollation = DEFAULT_COLLATION_OID;
+                       break;
+
+               case BOOLOID:
+                       att->attlen = 1;
+                       att->attbyval = true;
+                       att->attalign = 'c';
+                       att->attstorage = 'p';
+                       att->attcollation = InvalidOid;
+                       break;
+
+               case INT4OID:
+                       att->attlen = 4;
+                       att->attbyval = true;
+                       att->attalign = 'i';
+                       att->attstorage = 'p';
+                       att->attcollation = InvalidOid;
+                       break;
+       }
+}
+
 /*
  * TupleDescInitEntryCollation
  *

diff --git a/src/backend/replication/repl_gram.y b/src/backend/replication/repl_gram.y
index d962c768195eb251def2463c52073f70f563565f..b35d0f0cd1acc6cfbefe1d29b12f047005be63ea 100644 (file)
--- a/src/backend/replication/repl_gram.y
+++ b/src/backend/replication/repl_gram.y
@@ -61,6 +61,7 @@ Node *replication_parse_result;
 /* Keyword tokens. */
 %token K_BASE_BACKUP
 %token K_IDENTIFY_SYSTEM
+%token K_SHOW
 %token K_START_REPLICATION
 %token K_CREATE_REPLICATION_SLOT
 %token K_DROP_REPLICATION_SLOT
@@ -82,14 +83,14 @@ Node *replication_parse_result;
 %type <node>   command
 %type <node>   base_backup start_replication start_logical_replication
                                create_replication_slot drop_replication_slot identify_system
-                               timeline_history
+                               timeline_history show
 %type <list>   base_backup_opt_list
 %type <defelt> base_backup_opt
 %type <uintval>        opt_timeline
 %type <list>   plugin_options plugin_opt_list
 %type <defelt> plugin_opt_elem
 %type <node>   plugin_opt_arg
-%type <str>            opt_slot
+%type <str>            opt_slot var_name
 %type <boolval>        opt_reserve_wal opt_temporary
 
 %%
@@ -112,6 +113,7 @@ command:
                        | create_replication_slot
                        | drop_replication_slot
                        | timeline_history
+                       | show
                        ;
 
 /*
@@ -124,6 +126,22 @@ identify_system:
                                }
                        ;
 
+/*
+ * SHOW setting
+ */
+show:
+                       K_SHOW var_name
+                               {
+                                       VariableShowStmt *n = makeNode(VariableShowStmt);
+                                       n->name = $2;
+                                       $$ = (Node *) n;
+                               }
+
+var_name:      IDENT   { $$ = $1; }
+                       | var_name '.' IDENT
+                               { $$ = psprintf("%s.%s", $1, $3); }
+               ;
+
 /*
  * BASE_BACKUP [LABEL '<label>'] [PROGRESS] [FAST] [WAL] [NOWAIT]
  * [MAX_RATE %d] [TABLESPACE_MAP]

diff --git a/src/backend/replication/repl_scanner.l b/src/backend/replication/repl_scanner.l
index a3b5f926632eee4b34e0fbd73c6a93c3bda11539..37f857925e4b73ec13f40238e7bd3d632c169d79 100644 (file)
--- a/src/backend/replication/repl_scanner.l
+++ b/src/backend/replication/repl_scanner.l
@@ -83,6 +83,7 @@ identifier            {ident_start}{ident_cont}*
 BASE_BACKUP                    { return K_BASE_BACKUP; }
 FAST                   { return K_FAST; }
 IDENTIFY_SYSTEM                { return K_IDENTIFY_SYSTEM; }
+SHOW           { return K_SHOW; }
 LABEL                  { return K_LABEL; }
 NOWAIT                 { return K_NOWAIT; }
 PROGRESS                       { return K_PROGRESS; }

diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index f3082c379a5da5cc340dae01c9ee217881c1702d..5909b7dd8c5c5cbcbdcce3c50cefb9fd4321630d 100644 (file)
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -43,6 +43,7 @@
 #include <signal.h>
 #include <unistd.h>
 
+#include "access/printtup.h"
 #include "access/timeline.h"
 #include "access/transam.h"
 #include "access/xact.h"
@@ -72,11 +73,13 @@
 #include "storage/pmsignal.h"
 #include "storage/proc.h"
 #include "storage/procarray.h"
+#include "tcop/dest.h"
 #include "tcop/tcopprot.h"
 #include "utils/builtins.h"
 #include "utils/guc.h"
 #include "utils/memutils.h"
 #include "utils/pg_lsn.h"
+#include "utils/portal.h"
 #include "utils/ps_status.h"
 #include "utils/resowner.h"
 #include "utils/timeout.h"
@@ -1365,6 +1368,15 @@ exec_replication_command(const char *cmd_string)
                        SendTimeLineHistory((TimeLineHistoryCmd *) cmd_node);
                        break;
 
+               case T_VariableShowStmt:
+                       {
+                               DestReceiver *dest = CreateDestReceiver(DestRemoteSimple);
+                               VariableShowStmt *n = (VariableShowStmt *) cmd_node;
+
+                               GetPGVariable(n->name, dest);
+                       }
+                       break;
+
                default:
                        elog(ERROR, "unrecognized replication command node tag: %u",
                                 cmd_node->type);

diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 5f43b1ec928a0f04788ae7a8a2a4c61cab2aaa7f..74ca4e7432de10e4298628eceb6dbf5ef3fd4fa2 100644 (file)
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -7878,8 +7878,8 @@ ShowGUCConfigOption(const char *name, DestReceiver *dest)
 
        /* need a tuple descriptor representing a single TEXT column */
        tupdesc = CreateTemplateTupleDesc(1, false);
-       TupleDescInitEntry(tupdesc, (AttrNumber) 1, varname,
-                                          TEXTOID, -1, 0);
+       TupleDescInitBuiltinEntry(tupdesc, (AttrNumber) 1, varname,
+                                                         TEXTOID, -1, 0);
 
        /* prepare for projection of tuples */
        tstate = begin_tup_output_tupdesc(dest, tupdesc);
@@ -7905,12 +7905,12 @@ ShowAllGUCConfig(DestReceiver *dest)
 
        /* need a tuple descriptor representing three TEXT columns */
        tupdesc = CreateTemplateTupleDesc(3, false);
-       TupleDescInitEntry(tupdesc, (AttrNumber) 1, "name",
-                                          TEXTOID, -1, 0);
-       TupleDescInitEntry(tupdesc, (AttrNumber) 2, "setting",
-                                          TEXTOID, -1, 0);
-       TupleDescInitEntry(tupdesc, (AttrNumber) 3, "description",
-                                          TEXTOID, -1, 0);
+       TupleDescInitBuiltinEntry(tupdesc, (AttrNumber) 1, "name",
+                                                         TEXTOID, -1, 0);
+       TupleDescInitBuiltinEntry(tupdesc, (AttrNumber) 2, "setting",
+                                                         TEXTOID, -1, 0);
+       TupleDescInitBuiltinEntry(tupdesc, (AttrNumber) 3, "description",
+                                                         TEXTOID, -1, 0);
 
        /* prepare for projection of tuples */
        tstate = begin_tup_output_tupdesc(dest, tupdesc);

diff --git a/src/include/access/tupdesc.h b/src/include/access/tupdesc.h
index 0012877237ed81c209a67ba967f11eb6b1b9551d..b48f839028b8fbef6dcb5c81f54c7b4df4cbb220 100644 (file)
--- a/src/include/access/tupdesc.h
+++ b/src/include/access/tupdesc.h
@@ -119,6 +119,13 @@ extern void TupleDescInitEntry(TupleDesc desc,
                                   int32 typmod,
                                   int attdim);
 
+extern void TupleDescInitBuiltinEntry(TupleDesc desc,
+                                                 AttrNumber attributeNumber,
+                                                 const char *attributeName,
+                                                 Oid oidtypeid,
+                                                 int32 typmod,
+                                                 int attdim);
+
 extern void TupleDescInitEntryCollation(TupleDesc desc,
                                                        AttrNumber attributeNumber,
                                                        Oid collationid);