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Commit86f3169

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Add txid_current_ifassigned().
Add a variant of txid_current() that returns NULL if no transaction IDis assigned. This version can be used even on a standby server,although it will always return NULL since no transaction IDs can beassigned during recovery.Craig Ringer, per suggestion from Jim Nasby. Reviewed by Petr Jelinekand by me.
1 parentff36700 commit86f3169

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6 files changed

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6 files changed

+56
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‎doc/src/sgml/func.sgml‎

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@@ -17119,6 +17119,10 @@ SELECT collation for ('foo' COLLATE "de_DE");
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<primary>txid_current</primary>
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</indexterm>
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<indexterm>
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<primary>txid_current_if_assigned</primary>
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</indexterm>
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<indexterm>
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<primary>txid_current_snapshot</primary>
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</indexterm>
@@ -17159,6 +17163,11 @@ SELECT collation for ('foo' COLLATE "de_DE");
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<entry><type>bigint</type></entry>
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<entry>get current transaction ID, assigning a new one if the current transaction does not have one</entry>
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</row>
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<row>
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<entry><literal><function>txid_current_if_assigned()</function></literal></entry>
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<entry><type>bigint</type></entry>
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<entry>same as <function>txid_current()</function> but returns null instead of assigning an xid if none is already assigned</entry>
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</row>
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<row>
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<entry><literal><function>txid_current_snapshot()</function></literal></entry>
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<entry><type>txid_snapshot</type></entry>

‎src/backend/utils/adt/txid.c‎

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@@ -376,6 +376,27 @@ txid_current(PG_FUNCTION_ARGS)
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PG_RETURN_INT64(val);
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}
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/*
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* Same as txid_current() but doesn't assign a new xid if there isn't one
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* yet.
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*/
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Datum
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txid_current_if_assigned(PG_FUNCTION_ARGS)
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{
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txidval;
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TxidEpochstate;
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TransactionIdtopxid=GetTopTransactionIdIfAny();
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if (topxid==InvalidTransactionId)
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PG_RETURN_NULL();
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load_xid_epoch(&state);
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val=convert_xid(topxid,&state);
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PG_RETURN_INT64(val);
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}
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/*
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* txid_current_snapshot() returns txid_snapshot
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*

‎src/include/catalog/pg_proc.h‎

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@@ -4904,6 +4904,8 @@ DATA(insert OID = 2942 ( txid_snapshot_sendPGNSP PGUID 12 1 0 0 0 f f f f t
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DESCR("I/O");
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DATA(insert OID = 2943 ( txid_currentPGNSP PGUID 12 1 0 0 0 f f f f t f s u 0 0 20 "" _null_ _null_ _null_ _null_ _null_ txid_current _null_ _null_ _null_ ));
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DESCR("get current transaction ID");
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DATA(insert OID = 3348 ( txid_current_if_assignedPGNSP PGUID 12 1 0 0 0 f f f f t f s u 0 0 20 "" _null_ _null_ _null_ _null_ _null_ txid_current_if_assigned _null_ _null_ _null_ ));
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DESCR("get current transaction ID");
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DATA(insert OID = 2944 ( txid_current_snapshotPGNSP PGUID 12 1 0 0 0 f f f f t f s s 0 0 2970 "" _null_ _null_ _null_ _null_ _null_ txid_current_snapshot _null_ _null_ _null_ ));
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DESCR("get current snapshot");
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DATA(insert OID = 2945 ( txid_snapshot_xminPGNSP PGUID 12 1 0 0 0 f f f f t f i s 1 0 20 "2970" _null_ _null_ _null_ _null_ _null_ txid_snapshot_xmin _null_ _null_ _null_ ));

‎src/include/utils/builtins.h‎

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@@ -1221,6 +1221,7 @@ extern Datum txid_snapshot_out(PG_FUNCTION_ARGS);
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externDatumtxid_snapshot_recv(PG_FUNCTION_ARGS);
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externDatumtxid_snapshot_send(PG_FUNCTION_ARGS);
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externDatumtxid_current(PG_FUNCTION_ARGS);
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externDatumtxid_current_if_assigned(PG_FUNCTION_ARGS);
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externDatumtxid_current_snapshot(PG_FUNCTION_ARGS);
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externDatumtxid_snapshot_xmin(PG_FUNCTION_ARGS);
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externDatumtxid_snapshot_xmax(PG_FUNCTION_ARGS);

‎src/test/regress/expected/txid.out‎

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@@ -238,3 +238,19 @@ SELECT txid_snapshot '1:9223372036854775808:3';
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ERROR: invalid input syntax for type txid_snapshot: "1:9223372036854775808:3"
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LINE 1: SELECT txid_snapshot '1:9223372036854775808:3';
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^
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-- test txid_current_if_assigned
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BEGIN;
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SELECT txid_current_if_assigned() IS NULL;
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?column?
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----------
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t
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(1 row)
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SELECT txid_current() \gset
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SELECT txid_current_if_assigned() IS NOT DISTINCT FROM BIGINT :'txid_current';
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?column?
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----------
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t
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(1 row)
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COMMIT;

‎src/test/regress/sql/txid.sql‎

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@@ -52,3 +52,10 @@ select txid_visible_in_snapshot('1000100010001015', '1000100010001000:1000100010
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-- test 64bit overflow
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SELECT txid_snapshot'1:9223372036854775807:3';
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SELECT txid_snapshot'1:9223372036854775808:3';
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-- test txid_current_if_assigned
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BEGIN;
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SELECT txid_current_if_assigned() ISNULL;
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SELECT txid_current() \gset
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SELECT txid_current_if_assigned() IS NOT DISTINCTFROMBIGINT :'txid_current';
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COMMIT;

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