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robertmhaasrobertmhaas
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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
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lines changed

7 files changed

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‎doc/src/sgml/protocol.sgml

Lines changed: 24 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1393,6 +1393,30 @@ The commands accepted in walsender mode are:
13931393
</listitem>
13941394
</varlistentry>
13951395

1396+
<varlistentry>
1397+
<term><literal>SHOW</literal> <replaceable class="parameter">name</replaceable>
1398+
<indexterm><primary>SHOW</primary></indexterm>
1399+
</term>
1400+
<listitem>
1401+
<para>
1402+
Requests the server to send the current setting of a run-time parameter.
1403+
This is similar to the SQL command <xref linkend="sql-show">.
1404+
</para>
1405+
1406+
<variablelist>
1407+
<varlistentry>
1408+
<term><replaceable class="parameter">name</></term>
1409+
<listitem>
1410+
<para>
1411+
The name of a run-time parameter. Available parameters are documented
1412+
in <xref linkend="runtime-config">.
1413+
</para>
1414+
</listitem>
1415+
</varlistentry>
1416+
</variablelist>
1417+
</listitem>
1418+
</varlistentry>
1419+
13961420
<varlistentry>
13971421
<term><literal>TIMELINE_HISTORY</literal> <replaceable class="parameter">tli</replaceable>
13981422
<indexterm><primary>TIMELINE_HISTORY</primary></indexterm>

‎src/backend/access/common/tupdesc.c

Lines changed: 79 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -20,6 +20,7 @@
2020
#include "postgres.h"
2121

2222
#include "access/htup_details.h"
23+
#include "catalog/pg_collation.h"
2324
#include "catalog/pg_type.h"
2425
#include "miscadmin.h"
2526
#include "parser/parse_type.h"
@@ -553,6 +554,84 @@ TupleDescInitEntry(TupleDesc desc,
553554
ReleaseSysCache(tuple);
554555
}
555556

557+
/*
558+
* TupleDescInitBuiltinEntry
559+
* Initialize a tuple descriptor without catalog access. Only
560+
* a limited range of builtin types are supported.
561+
*/
562+
void
563+
TupleDescInitBuiltinEntry(TupleDesc desc,
564+
AttrNumber attributeNumber,
565+
const char *attributeName,
566+
Oid oidtypeid,
567+
int32 typmod,
568+
int attdim)
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{
570+
Form_pg_attribute att;
571+
572+
/* sanity checks */
573+
AssertArg(PointerIsValid(desc));
574+
AssertArg(attributeNumber >= 1);
575+
AssertArg(attributeNumber <= desc->natts);
576+
577+
/* initialize the attribute fields */
578+
att = desc->attrs[attributeNumber - 1];
579+
att->attrelid = 0; /* dummy value */
580+
581+
/* unlike TupleDescInitEntry, we require an attribute name */
582+
Assert(attributeName != NULL);
583+
namestrcpy(&(att->attname), attributeName);
584+
585+
att->attstattarget = -1;
586+
att->attcacheoff = -1;
587+
att->atttypmod = typmod;
588+
589+
att->attnum = attributeNumber;
590+
att->attndims = attdim;
591+
592+
att->attnotnull = false;
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att->atthasdef = false;
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att->attisdropped = false;
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att->attislocal = true;
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att->attinhcount = 0;
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/* attacl, attoptions and attfdwoptions are not present in tupledescs */
598+
599+
att->atttypid = oidtypeid;
600+
601+
/*
602+
* Our goal here is to support just enough types to let basic builtin
603+
* commands work without catalog access - e.g. so that we can do certain
604+
* things even in processes that are not connected to a database.
605+
*/
606+
switch (oidtypeid)
607+
{
608+
case TEXTOID:
609+
case TEXTARRAYOID:
610+
att->attlen = -1;
611+
att->attbyval = false;
612+
att->attalign = 'i';
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att->attstorage = 'x';
614+
att->attcollation = DEFAULT_COLLATION_OID;
615+
break;
616+
617+
case BOOLOID:
618+
att->attlen = 1;
619+
att->attbyval = true;
620+
att->attalign = 'c';
621+
att->attstorage = 'p';
622+
att->attcollation = InvalidOid;
623+
break;
624+
625+
case INT4OID:
626+
att->attlen = 4;
627+
att->attbyval = true;
628+
att->attalign = 'i';
629+
att->attstorage = 'p';
630+
att->attcollation = InvalidOid;
631+
break;
632+
}
633+
}
634+
556635
/*
557636
* TupleDescInitEntryCollation
558637
*

‎src/backend/replication/repl_gram.y

Lines changed: 20 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -61,6 +61,7 @@ Node *replication_parse_result;
6161
/* Keyword tokens. */
6262
%token K_BASE_BACKUP
6363
%token K_IDENTIFY_SYSTEM
64+
%token K_SHOW
6465
%token K_START_REPLICATION
6566
%token K_CREATE_REPLICATION_SLOT
6667
%token K_DROP_REPLICATION_SLOT
@@ -82,14 +83,14 @@ Node *replication_parse_result;
8283
%type <node> command
8384
%type <node> base_backup start_replication start_logical_replication
8485
create_replication_slot drop_replication_slot identify_system
85-
timeline_history
86+
timeline_history show
8687
%type <list> base_backup_opt_list
8788
%type <defelt> base_backup_opt
8889
%type <uintval> opt_timeline
8990
%type <list> plugin_options plugin_opt_list
9091
%type <defelt> plugin_opt_elem
9192
%type <node> plugin_opt_arg
92-
%type <str> opt_slot
93+
%type <str> opt_slot var_name
9394
%type <boolval> opt_reserve_wal opt_temporary
9495

9596
%%
@@ -112,6 +113,7 @@ command:
112113
| create_replication_slot
113114
| drop_replication_slot
114115
| timeline_history
116+
| show
115117
;
116118

117119
/*
@@ -124,6 +126,22 @@ identify_system:
124126
}
125127
;
126128

129+
/*
130+
* SHOW setting
131+
*/
132+
show:
133+
K_SHOW var_name
134+
{
135+
VariableShowStmt *n = makeNode(VariableShowStmt);
136+
n->name = $2;
137+
$$ = (Node *) n;
138+
}
139+
140+
var_name: IDENT { $$ = $1; }
141+
| var_name '.' IDENT
142+
{ $$ = psprintf("%s.%s", $1, $3); }
143+
;
144+
127145
/*
128146
* BASE_BACKUP [LABEL '<label>'] [PROGRESS] [FAST] [WAL] [NOWAIT]
129147
* [MAX_RATE %d] [TABLESPACE_MAP]

‎src/backend/replication/repl_scanner.l

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -83,6 +83,7 @@ identifier {ident_start}{ident_cont}*
8383
BASE_BACKUP { return K_BASE_BACKUP; }
8484
FAST { return K_FAST; }
8585
IDENTIFY_SYSTEM { return K_IDENTIFY_SYSTEM; }
86+
SHOW { return K_SHOW; }
8687
LABEL { return K_LABEL; }
8788
NOWAIT { return K_NOWAIT; }
8889
PROGRESS { return K_PROGRESS; }

‎src/backend/replication/walsender.c

Lines changed: 12 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -43,6 +43,7 @@
4343
#include <signal.h>
4444
#include <unistd.h>
4545

46+
#include "access/printtup.h"
4647
#include "access/timeline.h"
4748
#include "access/transam.h"
4849
#include "access/xact.h"
@@ -72,11 +73,13 @@
7273
#include "storage/pmsignal.h"
7374
#include "storage/proc.h"
7475
#include "storage/procarray.h"
76+
#include "tcop/dest.h"
7577
#include "tcop/tcopprot.h"
7678
#include "utils/builtins.h"
7779
#include "utils/guc.h"
7880
#include "utils/memutils.h"
7981
#include "utils/pg_lsn.h"
82+
#include "utils/portal.h"
8083
#include "utils/ps_status.h"
8184
#include "utils/resowner.h"
8285
#include "utils/timeout.h"
@@ -1365,6 +1368,15 @@ exec_replication_command(const char *cmd_string)
13651368
SendTimeLineHistory((TimeLineHistoryCmd *) cmd_node);
13661369
break;
13671370

1371+
case T_VariableShowStmt:
1372+
{
1373+
DestReceiver *dest = CreateDestReceiver(DestRemoteSimple);
1374+
VariableShowStmt *n = (VariableShowStmt *) cmd_node;
1375+
1376+
GetPGVariable(n->name, dest);
1377+
}
1378+
break;
1379+
13681380
default:
13691381
elog(ERROR, "unrecognized replication command node tag: %u",
13701382
cmd_node->type);

‎src/backend/utils/misc/guc.c

Lines changed: 8 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -7878,8 +7878,8 @@ ShowGUCConfigOption(const char *name, DestReceiver *dest)
78787878

78797879
/* need a tuple descriptor representing a single TEXT column */
78807880
tupdesc = CreateTemplateTupleDesc(1, false);
7881-
TupleDescInitEntry(tupdesc, (AttrNumber) 1, varname,
7882-
TEXTOID, -1, 0);
7881+
TupleDescInitBuiltinEntry(tupdesc, (AttrNumber) 1, varname,
7882+
TEXTOID, -1, 0);
78837883

78847884
/* prepare for projection of tuples */
78857885
tstate = begin_tup_output_tupdesc(dest, tupdesc);
@@ -7905,12 +7905,12 @@ ShowAllGUCConfig(DestReceiver *dest)
79057905

79067906
/* need a tuple descriptor representing three TEXT columns */
79077907
tupdesc = CreateTemplateTupleDesc(3, false);
7908-
TupleDescInitEntry(tupdesc, (AttrNumber) 1, "name",
7909-
TEXTOID, -1, 0);
7910-
TupleDescInitEntry(tupdesc, (AttrNumber) 2, "setting",
7911-
TEXTOID, -1, 0);
7912-
TupleDescInitEntry(tupdesc, (AttrNumber) 3, "description",
7913-
TEXTOID, -1, 0);
7908+
TupleDescInitBuiltinEntry(tupdesc, (AttrNumber) 1, "name",
7909+
TEXTOID, -1, 0);
7910+
TupleDescInitBuiltinEntry(tupdesc, (AttrNumber) 2, "setting",
7911+
TEXTOID, -1, 0);
7912+
TupleDescInitBuiltinEntry(tupdesc, (AttrNumber) 3, "description",
7913+
TEXTOID, -1, 0);
79147914

79157915
/* prepare for projection of tuples */
79167916
tstate = begin_tup_output_tupdesc(dest, tupdesc);

‎src/include/access/tupdesc.h

Lines changed: 7 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -119,6 +119,13 @@ extern void TupleDescInitEntry(TupleDesc desc,
119119
int32 typmod,
120120
int attdim);
121121

122+
extern void TupleDescInitBuiltinEntry(TupleDesc desc,
123+
AttrNumber attributeNumber,
124+
const char *attributeName,
125+
Oid oidtypeid,
126+
int32 typmod,
127+
int attdim);
128+
122129
extern void TupleDescInitEntryCollation(TupleDesc desc,
123130
AttrNumber attributeNumber,
124131
Oid collationid);

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