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Added the Skytools extended transaction ID module to contrib as discussed

Browse Source 
on CORE previously.

This module offers transaction ID's containing the original XID and the
transaction epoch as a bigint value to the user level. It also provides
a special txid_snapshot data type that contains an entire transactions
visibility snapshot information, which is useful to determine if a
particular txid was visible to a transaction or not.

The module has been tested by porting Slony-I from using its original
xxid data type.

Jan
REL8_3_STABLE
Jan Wieck 18 years ago
parent 2a997a7065
commit 1f92630fc4
8 changed files with 967 additions and 1 deletions
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  1. 3
      contrib/Makefile
  2. 26
      contrib/txid/Makefile
  3. 111
      contrib/txid/README.txid
  4. 212
      contrib/txid/expected/txid.out
  5. 58
      contrib/txid/sql/txid.sql
  6. 475
      contrib/txid/txid.c
  7. 68
      contrib/txid/txid.sql.in
  8. 15
      contrib/txid/uninstall_txid.sql

3
contrib/Makefile
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@ -1,4 +1,4 @@
# $PostgreSQL: pgsql/contrib/Makefile,v 1.78 2007/08/21 01:12:28 tgl Exp $
# $PostgreSQL: pgsql/contrib/Makefile,v 1.79 2007/10/07 23:32:19 wieck Exp $
subdir = contrib
top_builddir = ..
@ -30,6 +30,7 @@ WANTED_DIRS = \
pgstattuple \
seg \
spi \
txid \
tablefunc \
vacuumlo

26
contrib/txid/Makefile
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MODULES = txid
DATA_built = txid.sql
DATA = uninstall_txid.sql
DOCS = README.txid
REGRESS = txid
ifdef USE_PGXS
PG_CONFIG = pg_config
PGXS := $(shell $(PG_CONFIG) --pgxs)
include $(PGXS)
else
subdir = contrib/txid
top_builddir = ../..
include $(top_builddir)/src/Makefile.global
include $(top_srcdir)/contrib/contrib-global.mk
endif
test: install
$(MAKE) installcheck || { less regression.diffs; exit 1; }
ack:
cp results/* expected/

111
contrib/txid/README.txid
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txid - export transaction id's to user level
============================================
The goal is to make PostgreSQL internal transaction ID and snapshot
data usable externally. This allows very efficient queue
implementation done inside database.
[towrite: what snapshot means]
The module defines type txid_snapshot and following functions:
txid_current() returns int8
Current transaction ID.
txid_current_snapshot() returns txid_snapshot
Current snapshot.
txid_snapshot_xmin( snap ) returns int8
Smallest TXID in snapshot. TXID's smaller than this
are all visible in snapshot.
txid_snapshot_xmax( snap ) returns int8
Largest TXID in snapshot. TXID's starting from this one are
all invisible in snapshot.
txid_snapshot_xip( snap ) setof int8
List of in-progress TXID's in snapshot, that are invisible.
Values are between xmin and xmax.
txid_visible_in_snapshot(id, snap) returns bool
Is TXID visible in snapshot?
Fetching events
---------------
Lets say there is following event table:
CREATE TABLE events (
ev_txid int8 not null default txid_current(),
ev_data text
);
CREATE INDEX ev_txid_idx ON events (ev_txid);
Then event between 2 snapshots snap1 and snap2 can be fetched
with followign query:
SELECT ev_data FROM events
WHERE ev_txid >= txid_snapshot_xmin(:snap1)
AND ev_txid < txid_snapshot_xmax(:snap2)
AND NOT txid_visible_in_snapshot(ev_txid, :snap1)
AND txid_visible_in_snapshot(ev_txid, :snap2);
This is the simplest query but it has problem if there are long
transactions running - the txid_snapshot_xmin(snap1) will stay low
and the range will get very large.
This can be fixed by fetching only snap1.xmax ... snap1.xmax by range and
fetching possible txids below snap1.xmax explicitly:
SELECT ev_data FROM events
WHERE ((ev_txid >= txid_snapshot_xmax(:snap1) AND ev_txid < txid_snapshot_xmax(:snap2))
OR
(ev_txid IN (SELECT * FROM txid_snapshot_xip(:snap1))))
AND NOT txid_visible_in_snapshot(ev_txid, :snap1)
AND txid_visible_in_snapshot(ev_txid, :snap2);
Note that although the above queries work, the PostgreSQL fails to
plan them correctly. For actual usage the values for txid_snapshot_xmin,
txid_snapshot_xmax and txid_snapshot_xip should be filled in directly,
only then will they use index.
There are few more optimizations possible, like:
- Picking out only TXIDs that were actually committed between snap1 and snap2.
- Lowering the range from txid_snapshot_xmax(snap1) to decrease the list if TXIDs to be fetched separately.
To see example code for that it's best to see pgq.batch_event_sql() function in Skytools.
http://pgfoundry.org/projects/skytools/
Dumping and restoring data containing TXIDs.
--------------------------------------------
[towrite: reason for epoch increase]
You can look at current epoch with query:
SELECT txid_current() >> 32 as epoch;
So new epoch should be:
SELECT (txid_current() >> 32) + 1 as newepoch;
Epoch can be changed with pg_resetxlog command:
pg_resetxlog -e NEWEPOCH DATADIR
Database needs to be shut down for that moment.

212
contrib/txid/expected/txid.out
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-- init
\set ECHO none
-- i/o
select '12:13:'::txid_snapshot;
txid_snapshot
---------------
12:13:
(1 row)
select '12:13:1,2'::txid_snapshot;
ERROR: illegal txid_snapshot input format
-- errors
select '31:12:'::txid_snapshot;
ERROR: illegal txid_snapshot input format
select '0:1:'::txid_snapshot;
ERROR: illegal txid_snapshot input format
select '12:13:0'::txid_snapshot;
ERROR: illegal txid_snapshot input format
select '12:16:14,13'::txid_snapshot;
ERROR: illegal txid_snapshot input format
select '12:16:14,14'::txid_snapshot;
ERROR: illegal txid_snapshot input format
create table snapshot_test (
nr integer,
snap txid_snapshot
);
insert into snapshot_test values (1, '12:13:');
insert into snapshot_test values (2, '12:20:13,15,18');
insert into snapshot_test values (3, '100001:100009:100005,100007,100008');
insert into snapshot_test values (4, '100:150:101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,123,124,125,126,127,128,129,130,131');
select snap from snapshot_test order by nr;
snap
-------------------------------------------------------------------------------------------------------------------------------------
12:13:
12:20:13,15,18
100001:100009:100005,100007,100008
100:150:101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,123,124,125,126,127,128,129,130,131
(4 rows)
select txid_snapshot_xmin(snap),
txid_snapshot_xmax(snap),
txid_snapshot_xip(snap)
from snapshot_test order by nr;
txid_snapshot_xmin | txid_snapshot_xmax | txid_snapshot_xip
--------------------+--------------------+-------------------
12 | 20 | 13
12 | 20 | 15
12 | 20 | 18
100001 | 100009 | 100005
100001 | 100009 | 100007
100001 | 100009 | 100008
100 | 150 | 101
100 | 150 | 102
100 | 150 | 103
100 | 150 | 104
100 | 150 | 105
100 | 150 | 106
100 | 150 | 107
100 | 150 | 108
100 | 150 | 109
100 | 150 | 110
100 | 150 | 111
100 | 150 | 112
100 | 150 | 113
100 | 150 | 114
100 | 150 | 115
100 | 150 | 116
100 | 150 | 117
100 | 150 | 118
100 | 150 | 119
100 | 150 | 120
100 | 150 | 121
100 | 150 | 122
100 | 150 | 123
100 | 150 | 124
100 | 150 | 125
100 | 150 | 126
100 | 150 | 127
100 | 150 | 128
100 | 150 | 129
100 | 150 | 130
100 | 150 | 131
(37 rows)
select id, txid_visible_in_snapshot(id, snap)
from snapshot_test, generate_series(11, 21) id
where nr = 2;
id | txid_visible_in_snapshot
----+--------------------------
11 | t
12 | t
13 | f
14 | t
15 | f
16 | t
17 | t
18 | f
19 | t
20 | f
21 | f
(11 rows)
-- test bsearch
select id, txid_visible_in_snapshot(id, snap)
from snapshot_test, generate_series(90, 160) id
where nr = 4;
id | txid_visible_in_snapshot
-----+--------------------------
90 | t
91 | t
92 | t
93 | t
94 | t
95 | t
96 | t
97 | t
98 | t
99 | t
100 | t
101 | f
102 | f
103 | f
104 | f
105 | f
106 | f
107 | f
108 | f
109 | f
110 | f
111 | f
112 | f
113 | f
114 | f
115 | f
116 | f
117 | f
118 | f
119 | f
120 | f
121 | f
122 | f
123 | f
124 | f
125 | f
126 | f
127 | f
128 | f
129 | f
130 | f
131 | f
132 | t
133 | t
134 | t
135 | t
136 | t
137 | t
138 | t
139 | t
140 | t
141 | t
142 | t
143 | t
144 | t
145 | t
146 | t
147 | t
148 | t
149 | t
150 | f
151 | f
152 | f
153 | f
154 | f
155 | f
156 | f
157 | f
158 | f
159 | f
160 | f
(71 rows)
-- test current values also
select txid_current() >= txid_snapshot_xmin(txid_current_snapshot());
?column?
----------
t
(1 row)
/* due to lazy xid alloc in 8.3 those are different in 8.2 and 8.3
select txid_current() < txid_snapshot_xmax(txid_current_snapshot());
select txid_visible_in_snapshot(txid_current(), txid_current_snapshot());
*/
-- test 64bitness
select txid_snapshot '1000100010001000:1000100010001100:1000100010001012,1000100010001013';
txid_snapshot
---------------------------------------------------------------------
1000100010001000:1000100010001100:1000100010001012,1000100010001013
(1 row)
select txid_visible_in_snapshot('1000100010001012', '1000100010001000:1000100010001100:1000100010001012,1000100010001013');
txid_visible_in_snapshot
--------------------------
f
(1 row)
select txid_visible_in_snapshot('1000100010001015', '1000100010001000:1000100010001100:1000100010001012,1000100010001013');
txid_visible_in_snapshot
--------------------------
t
(1 row)

58
contrib/txid/sql/txid.sql
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-- init
\set ECHO none
set client_min_messages = 'warning';
\i txid.sql
set client_min_messages = 'notice';
\set ECHO all
-- i/o
select '12:13:'::txid_snapshot;
select '12:13:1,2'::txid_snapshot;
-- errors
select '31:12:'::txid_snapshot;
select '0:1:'::txid_snapshot;
select '12:13:0'::txid_snapshot;
select '12:16:14,13'::txid_snapshot;
select '12:16:14,14'::txid_snapshot;
create table snapshot_test (
nr integer,
snap txid_snapshot
);
insert into snapshot_test values (1, '12:13:');
insert into snapshot_test values (2, '12:20:13,15,18');
insert into snapshot_test values (3, '100001:100009:100005,100007,100008');
insert into snapshot_test values (4, '100:150:101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,123,124,125,126,127,128,129,130,131');
select snap from snapshot_test order by nr;
select txid_snapshot_xmin(snap),
txid_snapshot_xmax(snap),
txid_snapshot_xip(snap)
from snapshot_test order by nr;
select id, txid_visible_in_snapshot(id, snap)
from snapshot_test, generate_series(11, 21) id
where nr = 2;
-- test bsearch
select id, txid_visible_in_snapshot(id, snap)
from snapshot_test, generate_series(90, 160) id
where nr = 4;
-- test current values also
select txid_current() >= txid_snapshot_xmin(txid_current_snapshot());
/* due to lazy xid alloc in 8.3 those are different in 8.2 and 8.3
select txid_current() < txid_snapshot_xmax(txid_current_snapshot());
select txid_visible_in_snapshot(txid_current(), txid_current_snapshot());
*/
-- test 64bitness
select txid_snapshot '1000100010001000:1000100010001100:1000100010001012,1000100010001013';
select txid_visible_in_snapshot('1000100010001012', '1000100010001000:1000100010001100:1000100010001012,1000100010001013');
select txid_visible_in_snapshot('1000100010001015', '1000100010001000:1000100010001100:1000100010001012,1000100010001013');

475
contrib/txid/txid.c
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/*-------------------------------------------------------------------------
* txid.c
*
* Export backend internal tranasction id's to user level.
*
* Copyright (c) 2003-2007, PostgreSQL Global Development Group
* Author: Jan Wieck, Afilias USA INC.
*
* 64-bit txids: Marko Kreen, Skype Technologies
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/transam.h"
#include "access/xact.h"
#include "funcapi.h"
#ifdef PG_MODULE_MAGIC
PG_MODULE_MAGIC;
#endif
#ifdef INT64_IS_BUSTED
#error txid needs working int64
#endif
/* txid will be signed int8 in database */
#define MAX_TXID UINT64CONST(0x7FFFFFFFFFFFFFFF)
/*
* If defined, use bsearch() function for searching
* txid's inside snapshots that have more than given values.
*/
#define USE_BSEARCH_IF_NXIP_GREATER 30
/* format code for uint64 to appendStringInfo */
#define TXID_FMT UINT64_FORMAT
/* Use unsigned variant internally */
typedef uint64 txid;
/*
* Snapshot for 8byte txids.
*/
typedef struct
{
/*
* 4-byte length hdr, should not be touched directly.
*
* Explicit embedding is ok as we want always correct
* alignment anyway.
*/
int32 __varsz;
uint32 nxip; /* number of txids in xip array */
txid xmin;
txid xmax;
txid xip[1]; /* in-progress txids */
} TxidSnapshot;
#define TXID_SNAPSHOT_SIZE(nxip) (offsetof(TxidSnapshot, xip) + sizeof(txid) * (nxip))
/*
* Epoch values from backend.
*/
typedef struct {
uint64 last_value;
uint64 epoch;
} TxidEpoch;
/* public functions */
Datum txid_snapshot_in(PG_FUNCTION_ARGS);
Datum txid_snapshot_out(PG_FUNCTION_ARGS);
Datum txid_current(PG_FUNCTION_ARGS);
Datum txid_current_snapshot(PG_FUNCTION_ARGS);
Datum txid_snapshot_xmin(PG_FUNCTION_ARGS);
Datum txid_snapshot_xmax(PG_FUNCTION_ARGS);
Datum txid_snapshot_xip(PG_FUNCTION_ARGS);
Datum txid_visible_in_snapshot(PG_FUNCTION_ARGS);
/* public function tags */
PG_FUNCTION_INFO_V1(txid_snapshot_in);
PG_FUNCTION_INFO_V1(txid_snapshot_out);
PG_FUNCTION_INFO_V1(txid_current);
PG_FUNCTION_INFO_V1(txid_current_snapshot);
PG_FUNCTION_INFO_V1(txid_snapshot_xmin);
PG_FUNCTION_INFO_V1(txid_snapshot_xmax);
PG_FUNCTION_INFO_V1(txid_snapshot_xip);
PG_FUNCTION_INFO_V1(txid_visible_in_snapshot);
/*
* do a TransactionId -> txid conversion
*/
static txid
convert_xid(TransactionId xid, const TxidEpoch *state)
{
uint64 epoch;
/* return special xid's as-is */
if (xid < FirstNormalTransactionId)
return xid;
/* xid can on both sides on wrap-around */
epoch = state->epoch;
if (TransactionIdPrecedes(xid, state->last_value)) {
if (xid > state->last_value)
epoch--;
} else if (TransactionIdFollows(xid, state->last_value)) {
if (xid < state->last_value)
epoch++;
}
return (epoch << 32) | xid;
}
/*
* Fetch epoch data from backend.
*/
static void
load_xid_epoch(TxidEpoch *state)
{
TransactionId xid;
uint32 epoch;
GetNextXidAndEpoch(&xid, &epoch);
state->epoch = epoch;
state->last_value = xid;
}
/*
* compare txid in memory.
*/
static int
cmp_txid(const void *aa, const void *bb)
{
const uint64 *a = aa;
const uint64 *b = bb;
if (*a < *b)
return -1;
if (*a > *b)
return 1;
return 0;
}
/*
* order txids, for bsearch().
*/
static void
sort_snapshot(TxidSnapshot *snap)
{
if (snap->nxip > 1)
qsort(snap->xip, snap->nxip, sizeof(txid), cmp_txid);
}
/*
* check txid visibility.
*/
static bool
is_visible_txid(txid value, const TxidSnapshot *snap)
{
if (value < snap->xmin)
return true;
else if (value >= snap->xmax)
return false;
#ifdef USE_BSEARCH_IF_NXIP_GREATER
else if (snap->nxip > USE_BSEARCH_IF_NXIP_GREATER)
{
void *res;
res = bsearch(&value, snap->xip, snap->nxip, sizeof(txid), cmp_txid);
return (res) ? false : true;
}
#endif
else
{
int i;
for (i = 0; i < snap->nxip; i++)
{
if (value == snap->xip[i])
return false;
}
return true;
}
}
/*
* helper functions to use StringInfo for TxidSnapshot creation.
*/
static StringInfo
buf_init(txid xmin, txid xmax)
{
TxidSnapshot snap;
StringInfo buf;
snap.xmin = xmin;
snap.xmax = xmax;
snap.nxip = 0;
buf = makeStringInfo();
appendBinaryStringInfo(buf, (char *)&snap, TXID_SNAPSHOT_SIZE(0));
return buf;
}
static void
buf_add_txid(StringInfo buf, txid xid)
{
TxidSnapshot *snap = (TxidSnapshot *)buf->data;
/* do it before possible realloc */
snap->nxip++;
appendBinaryStringInfo(buf, (char *)&xid, sizeof(xid));
}
static TxidSnapshot *
buf_finalize(StringInfo buf)
{
TxidSnapshot *snap = (TxidSnapshot *)buf->data;
SET_VARSIZE(snap, buf->len);
/* buf is not needed anymore */
buf->data = NULL;
pfree(buf);
return snap;
}
/*
* parse snapshot from cstring
*/
static TxidSnapshot *
parse_snapshot(const char *str)
{
txid xmin;
txid xmax;
txid last_val = 0, val;
char *endp;
StringInfo buf;
xmin = (txid) strtoull(str, &endp, 0);
if (*endp != ':')
goto bad_format;
str = endp + 1;
xmax = (txid) strtoull(str, &endp, 0);
if (*endp != ':')
goto bad_format;
str = endp + 1;
/* it should look sane */
if (xmin > xmax || xmin == 0 || xmax > MAX_TXID)
goto bad_format;
/* allocate buffer */
buf = buf_init(xmin, xmax);
/* loop over values */
while (*str != '\0')
{
/* read next value */
val = (txid) strtoull(str, &endp, 0);
str = endp;
/* require the input to be in order */
if (val < xmin || val <= last_val || val >= xmax)
goto bad_format;
buf_add_txid(buf, val);
last_val = val;
if (*str == ',')
str++;
else if (*str != '\0')
goto bad_format;
}
return buf_finalize(buf);
bad_format:
elog(ERROR, "illegal txid_snapshot input format");
return NULL;
}
/*
* Public functions
*/
/*
* txid_current() returns int8
*
* Return the current transaction ID
*/
Datum
txid_current(PG_FUNCTION_ARGS)
{
txid val;
TxidEpoch state;
load_xid_epoch(&state);
val = convert_xid(GetTopTransactionId(), &state);
PG_RETURN_INT64(val);
}
/*
* txid_current_snapshot() returns txid_snapshot
*
* Return current snapshot
*/
Datum
txid_current_snapshot(PG_FUNCTION_ARGS)
{
TxidSnapshot *snap;
unsigned nxip, i, size;
TxidEpoch state;
Snapshot cur;
cur = SerializableSnapshot;
if (cur == NULL)
elog(ERROR, "get_current_snapshot: SerializableSnapshot == NULL");
load_xid_epoch(&state);
/* allocate */
nxip = cur->xcnt;
size = TXID_SNAPSHOT_SIZE(nxip);
snap = palloc(size);
SET_VARSIZE(snap, size);
/* fill */
snap->xmin = convert_xid(cur->xmin, &state);
snap->xmax = convert_xid(cur->xmax, &state);
snap->nxip = nxip;
for (i = 0; i < nxip; i++)
snap->xip[i] = convert_xid(cur->xip[i], &state);
/* we want them guaranteed ascending order */
sort_snapshot(snap);
PG_RETURN_POINTER(snap);
}
/*
* txid_snapshot_in(cstring) returns txid_snapshot
*
* input function for type txid_snapshot
*/
Datum
txid_snapshot_in(PG_FUNCTION_ARGS)
{
TxidSnapshot *snap;
char *str = PG_GETARG_CSTRING(0);
snap = parse_snapshot(str);
PG_RETURN_POINTER(snap);
}
/*
* txid_snapshot_out(txid_snapshot) returns cstring
*
* output function for type txid_snapshot
*/
Datum
txid_snapshot_out(PG_FUNCTION_ARGS)
{
TxidSnapshot *snap;
StringInfoData str;
int i;
snap = (TxidSnapshot *) PG_GETARG_VARLENA_P(0);
initStringInfo(&str);
appendStringInfo(&str, TXID_FMT ":", snap->xmin);
appendStringInfo(&str, TXID_FMT ":", snap->xmax);
for (i = 0; i < snap->nxip; i++)
{
appendStringInfo(&str, "%s" TXID_FMT,
((i > 0) ? "," : ""),
snap->xip[i]);
}
PG_FREE_IF_COPY(snap, 0);
PG_RETURN_CSTRING(str.data);
}
/*
* txid_visible_in_snapshot(int8, txid_snapshot) returns bool
*
* is txid visible in snapshot ?
*/
Datum
txid_visible_in_snapshot(PG_FUNCTION_ARGS)
{
txid value = PG_GETARG_INT64(0);
TxidSnapshot *snap = (TxidSnapshot *) PG_GETARG_VARLENA_P(1);
int res;
res = is_visible_txid(value, snap) ? true : false;
PG_FREE_IF_COPY(snap, 1);
PG_RETURN_BOOL(res);
}
/*
* txid_snapshot_xmin(txid_snapshot) returns int8
*
* return snapshot's xmin
*/
Datum
txid_snapshot_xmin(PG_FUNCTION_ARGS)
{
TxidSnapshot *snap = (TxidSnapshot *) PG_GETARG_VARLENA_P(0);
txid res = snap->xmin;
PG_FREE_IF_COPY(snap, 0);
PG_RETURN_INT64(res);
}
/*
* txid_snapshot_xmax(txid_snapshot) returns int8
*
* return snapshot's xmax
*/
Datum
txid_snapshot_xmax(PG_FUNCTION_ARGS)
{
TxidSnapshot *snap = (TxidSnapshot *) PG_GETARG_VARLENA_P(0);
txid res = snap->xmax;
PG_FREE_IF_COPY(snap, 0);
PG_RETURN_INT64(res);
}
/*
* txid_snapshot_xip(txid_snapshot) returns setof int8
*
* return in-progress TXIDs in snapshot.
*/
Datum
txid_snapshot_xip(PG_FUNCTION_ARGS)
{
FuncCallContext *fctx;
TxidSnapshot *snap;
txid value;
/* on first call initialize snap_state and get copy of snapshot */
if (SRF_IS_FIRSTCALL()) {
TxidSnapshot *arg;
fctx = SRF_FIRSTCALL_INIT();
/* make a copy of user snapshot */
arg = (TxidSnapshot *) PG_GETARG_VARLENA_P(0);
snap = MemoryContextAlloc(fctx->multi_call_memory_ctx, VARSIZE(arg));
memcpy(snap, arg, VARSIZE(arg));
PG_FREE_IF_COPY(arg, 0);
fctx->user_fctx = snap;
}
/* return values one-by-one */
fctx = SRF_PERCALL_SETUP();
snap = fctx->user_fctx;
if (fctx->call_cntr < snap->nxip) {
value = snap->xip[fctx->call_cntr];
SRF_RETURN_NEXT(fctx, Int64GetDatum(value));
} else {
SRF_RETURN_DONE(fctx);
}
}

68
contrib/txid/txid.sql.in
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-- ----------
-- txid.sql
--
-- SQL script for loading the transaction ID compatible datatype
--
-- Copyright (c) 2003-2007, PostgreSQL Global Development Group
-- Author: Jan Wieck, Afilias USA INC.
--
-- 64-bit txids: Marko Kreen, Skype Technologies
-- ----------
--
-- A special transaction snapshot data type for faster visibility checks
--
CREATE OR REPLACE FUNCTION txid_snapshot_in(cstring)
RETURNS txid_snapshot
AS 'MODULE_PATHNAME' LANGUAGE C
IMMUTABLE STRICT;
CREATE OR REPLACE FUNCTION txid_snapshot_out(txid_snapshot)
RETURNS cstring
AS 'MODULE_PATHNAME' LANGUAGE C
IMMUTABLE STRICT;
--
-- The data type itself
--
CREATE TYPE txid_snapshot (
INPUT = txid_snapshot_in,
OUTPUT = txid_snapshot_out,
INTERNALLENGTH = variable,
STORAGE = extended,
ALIGNMENT = double
);
CREATE OR REPLACE FUNCTION txid_current()
RETURNS bigint
AS 'MODULE_PATHNAME', 'txid_current' LANGUAGE C
STABLE;
CREATE OR REPLACE FUNCTION txid_current_snapshot()
RETURNS txid_snapshot
AS 'MODULE_PATHNAME', 'txid_current_snapshot' LANGUAGE C
STABLE;
CREATE OR REPLACE FUNCTION txid_snapshot_xmin(txid_snapshot)
RETURNS bigint
AS 'MODULE_PATHNAME', 'txid_snapshot_xmin' LANGUAGE C
IMMUTABLE STRICT;
CREATE OR REPLACE FUNCTION txid_snapshot_xmax(txid_snapshot)
RETURNS bigint
AS 'MODULE_PATHNAME', 'txid_snapshot_xmax' LANGUAGE C
IMMUTABLE STRICT;
CREATE OR REPLACE FUNCTION txid_snapshot_xip(txid_snapshot)
RETURNS setof bigint
AS 'MODULE_PATHNAME', 'txid_snapshot_xip' LANGUAGE C
IMMUTABLE STRICT;
--
-- Special comparision functions for visibility checks
--
CREATE OR REPLACE FUNCTION txid_visible_in_snapshot(bigint, txid_snapshot)
RETURNS boolean
AS 'MODULE_PATHNAME', 'txid_visible_in_snapshot' LANGUAGE C
IMMUTABLE STRICT;

15
contrib/txid/uninstall_txid.sql
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DROP FUNCTION txid_current();
DROP FUNCTION txid_current_snapshot();
DROP FUNCTION txid_snapshot_xmin(txid_snapshot);
DROP FUNCTION txid_snapshot_xmax(txid_snapshot);
DROP FUNCTION txid_snapshot_xip(txid_snapshot);
DROP FUNCTION txid_visible_in_snapshot(bigint, txid_snapshot);
DROP FUNCTION txid_not_visible_in_snapshot(bigint, txid_snapshot);
DROP TYPE txid_snapshot cascade;
-- need cascade to drop those:
-- DROP FUNCTION txid_snapshot_in(cstring);
-- DROP FUNCTION txid_snapshot_out(txid_snapshot);
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