From d1ecd539477fe640455dc890216a7c1561e047b4 Mon Sep 17 00:00:00 2001
From: Robert Haas <rhaas@postgresql.org>
Date: Tue, 24 Jan 2017 16:59:18 -0500
Subject: [PATCH] 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
---
doc/src/sgml/protocol.sgml | 24 ++++++++
src/backend/access/common/tupdesc.c | 79 ++++++++++++++++++++++++++
src/backend/replication/repl_gram.y | 22 ++++++-
src/backend/replication/repl_scanner.l | 1 +
src/backend/replication/walsender.c | 12 ++++
src/backend/utils/misc/guc.c | 16 +++---
src/include/access/tupdesc.h | 7 +++
7 files changed, 151 insertions(+), 10 deletions(-)
diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index 5f89db5857..028ef10d91 100644
--- 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 54a32c0223..083c0303dc 100644
--- 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 d962c76819..b35d0f0cd1 100644
--- 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 a3b5f92663..37f857925e 100644
--- 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 f3082c379a..5909b7dd8c 100644
--- 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 5f43b1ec92..74ca4e7432 100644
--- 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 0012877237..b48f839028 100644
--- 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);
--
2.40.0