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
-# $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 = ..
pgstattuple \
seg \
spi \
+ txid \
tablefunc \
vacuumlo
--- /dev/null
+
+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/
+
--- /dev/null
+
+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.
+
+
--- /dev/null
+-- 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)
+
--- /dev/null
+-- 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');
+
--- /dev/null
+/*-------------------------------------------------------------------------
+ * 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);
+ }
+}
+
--- /dev/null
+-- ----------
+-- 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;
+
--- /dev/null
+
+
+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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