Introduce xid8-based functions to replace txid_XXX.

The txid_XXX family of fmgr functions exposes 64 bit transaction IDs to
users as int8.  Now that we have an SQL type xid8 for FullTransactionId,
define a new set of functions including pg_current_xact_id() and
pg_current_snapshot() based on that.  Keep the old functions around too,
for now.

It's a bit sneaky to use the same C functions for both, but since the
binary representation is identical except for the signedness of the
type, and since older functions are the ones using the wrong signedness,
and since we'll presumably drop the older ones after a reasonable period
of time, it seems reasonable to switch to FullTransactionId internally
and share the code for both.

Reviewed-by: Fujii Masao <[email protected]>
Reviewed-by: Takao Fujii <[email protected]>
Reviewed-by: Yoshikazu Imai <[email protected]>
Reviewed-by: Mark Dilger <[email protected]>
Discussion: https://postgr.es/m/20190725000636.666m5mad25wfbrri%40alap3.anarazel.de

Author: macdice

contrib/test_decoding/expected/ddl.out

@@ -382,7 +382,7 @@ SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'inc
 -- test whether a known, but not yet logged toplevel xact, followed by a
 -- subxact commit is handled correctly
 BEGIN;
-SELECT txid_current() != 0; -- so no fixed xid apears in the outfile
+SELECT pg_current_xact_id() != '0'; -- so no fixed xid apears in the outfile
  ?column? 
 ----------
  t

contrib/test_decoding/expected/decoding_in_xact.out

@@ -2,7 +2,7 @@
 SET synchronous_commit = on;
 -- fail because we're creating a slot while in an xact with xid
 BEGIN;
-SELECT txid_current() = 0;
+SELECT pg_current_xact_id() = '0';
  ?column? 
 ----------
  f
@@ -13,7 +13,7 @@ ERROR:  cannot create logical replication slot in transaction that has performed
 ROLLBACK;
 -- fail because we're creating a slot while in a subxact whose topxact has an xid
 BEGIN;
-SELECT txid_current() = 0;
+SELECT pg_current_xact_id() = '0';
  ?column? 
 ----------
  f
@@ -50,7 +50,7 @@ CREATE TABLE nobarf(id serial primary key, data text);
 INSERT INTO nobarf(data) VALUES('1');
 -- decoding works in transaction with xid
 BEGIN;
-SELECT txid_current() = 0;
+SELECT pg_current_xact_id() = '0';
  ?column? 
 ----------
  f

contrib/test_decoding/expected/oldest_xmin.out

@@ -2,7 +2,7 @@ Parsed test spec with 2 sessions
 
 starting permutation: s0_begin s0_getxid s1_begin s1_insert s0_alter s0_commit s0_checkpoint s0_get_changes s0_get_changes s1_commit s0_vacuum s0_get_changes
 step s0_begin: BEGIN;
-step s0_getxid: SELECT txid_current() IS NULL;
+step s0_getxid: SELECT pg_current_xact_id() IS NULL;
 ?column?       
 
 f              

contrib/test_decoding/expected/ondisk_startup.out

@@ -2,20 +2,20 @@ Parsed test spec with 3 sessions
 
 starting permutation: s2b s2txid s1init s3b s3txid s2alter s2c s2b s2txid s3c s2c s1insert s1checkpoint s1start s1insert s1alter s1insert s1start
 step s2b: BEGIN;
-step s2txid: SELECT txid_current() IS NULL;
+step s2txid: SELECT pg_current_xact_id() IS NULL;
 ?column?       
 
 f              
 step s1init: SELECT 'init' FROM pg_create_logical_replication_slot('isolation_slot', 'test_decoding'); <waiting ...>
 step s3b: BEGIN;
-step s3txid: SELECT txid_current() IS NULL;
+step s3txid: SELECT pg_current_xact_id() IS NULL;
 ?column?       
 
 f              
 step s2alter: ALTER TABLE do_write ADD COLUMN addedbys2 int;
 step s2c: COMMIT;
 step s2b: BEGIN;
-step s2txid: SELECT txid_current() IS NULL;
+step s2txid: SELECT pg_current_xact_id() IS NULL;
 ?column?       
 
 f              

contrib/test_decoding/expected/snapshot_transfer.out

@@ -3,7 +3,7 @@ Parsed test spec with 2 sessions
 starting permutation: s0_begin s0_begin_sub0 s0_log_assignment s0_sub_get_base_snap s1_produce_new_snap s0_insert s0_end_sub0 s0_commit s0_get_changes
 step s0_begin: BEGIN;
 step s0_begin_sub0: SAVEPOINT s0;
-step s0_log_assignment: SELECT txid_current() IS NULL;
+step s0_log_assignment: SELECT pg_current_xact_id() IS NULL;
 ?column?       
 
 f              
@@ -26,7 +26,7 @@ stop
 starting permutation: s0_begin s0_begin_sub0 s0_log_assignment s0_begin_sub1 s0_sub_get_base_snap s1_produce_new_snap s0_insert s0_end_sub1 s0_end_sub0 s0_commit s0_get_changes
 step s0_begin: BEGIN;
 step s0_begin_sub0: SAVEPOINT s0;
-step s0_log_assignment: SELECT txid_current() IS NULL;
+step s0_log_assignment: SELECT pg_current_xact_id() IS NULL;
 ?column?       
 
 f              

contrib/test_decoding/specs/oldest_xmin.spec

@@ -19,7 +19,7 @@ teardown
 session "s0"
 setup { SET synchronous_commit=on; }
 step "s0_begin" { BEGIN; }
-step "s0_getxid" { SELECT txid_current() IS NULL; }
+step "s0_getxid" { SELECT pg_current_xact_id() IS NULL; }
 step "s0_alter" { ALTER TYPE basket DROP ATTRIBUTE mangos; }
 step "s0_commit" { COMMIT; }
 step "s0_checkpoint" { CHECKPOINT; }

contrib/test_decoding/specs/ondisk_startup.spec

@@ -25,7 +25,7 @@ session "s2"
 setup { SET synchronous_commit=on; }
 
 step "s2b" { BEGIN; }
-step "s2txid" { SELECT txid_current() IS NULL; }
+step "s2txid" { SELECT pg_current_xact_id() IS NULL; }
 step "s2alter" { ALTER TABLE do_write ADD COLUMN addedbys2 int; }
 step "s2c" { COMMIT; }
 
@@ -34,7 +34,7 @@ session "s3"
 setup { SET synchronous_commit=on; }
 
 step "s3b" { BEGIN; }
-step "s3txid" { SELECT txid_current() IS NULL; }
+step "s3txid" { SELECT pg_current_xact_id() IS NULL; }
 step "s3c" { COMMIT; }
 
 # Force usage of ondisk snapshot by starting and not finishing a

contrib/test_decoding/specs/snapshot_transfer.spec

@@ -20,7 +20,7 @@ session "s0"
 setup { SET synchronous_commit=on; }
 step "s0_begin" { BEGIN; }
 step "s0_begin_sub0" { SAVEPOINT s0; }
-step "s0_log_assignment" { SELECT txid_current() IS NULL; }
+step "s0_log_assignment" { SELECT pg_current_xact_id() IS NULL; }
 step "s0_begin_sub1" { SAVEPOINT s1; }
 step "s0_sub_get_base_snap" { INSERT INTO dummy VALUES (0); }
 step "s0_insert" { INSERT INTO harvest VALUES (1, 2, 3); }

contrib/test_decoding/sql/ddl.sql

@@ -220,7 +220,7 @@ SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'inc
 -- test whether a known, but not yet logged toplevel xact, followed by a
 -- subxact commit is handled correctly
 BEGIN;
-SELECT txid_current() != 0; -- so no fixed xid apears in the outfile
+SELECT pg_current_xact_id() != '0'; -- so no fixed xid apears in the outfile
 SAVEPOINT a;
 INSERT INTO tr_sub(path) VALUES ('4-top-1-#1');
 RELEASE SAVEPOINT a;

contrib/test_decoding/sql/decoding_in_xact.sql

@@ -3,13 +3,13 @@ SET synchronous_commit = on;
 
 -- fail because we're creating a slot while in an xact with xid
 BEGIN;
-SELECT txid_current() = 0;
+SELECT pg_current_xact_id() = '0';
 SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
 ROLLBACK;
 
 -- fail because we're creating a slot while in a subxact whose topxact has an xid
 BEGIN;
-SELECT txid_current() = 0;
+SELECT pg_current_xact_id() = '0';
 SAVEPOINT barf;
 SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
 ROLLBACK TO SAVEPOINT barf;
@@ -29,7 +29,7 @@ INSERT INTO nobarf(data) VALUES('1');
 
 -- decoding works in transaction with xid
 BEGIN;
-SELECT txid_current() = 0;
+SELECT pg_current_xact_id() = '0';
 -- don't show yet, haven't committed
 INSERT INTO nobarf(data) VALUES('2');
 SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');

doc/src/sgml/datatype.sgml

@@ -198,6 +198,12 @@
        <entry><productname>PostgreSQL</productname> Log Sequence Number</entry>
       </row>
 
+      <row>
+       <entry><type>pg_snapshot</type></entry>
+       <entry></entry>
+       <entry>user-level transaction ID snapshot</entry>
+      </row>
+
       <row>
        <entry><type>point</type></entry>
        <entry></entry>
@@ -279,7 +285,7 @@
       <row>
        <entry><type>txid_snapshot</type></entry>
        <entry></entry>
-       <entry>user-level transaction ID snapshot</entry>
+       <entry>user-level transaction ID snapshot (deprecated; see <type>pg_snapshot</type>)</entry>
       </row>
 
       <row>