Code review for txid patch: add binary I/O functions, avoid dependence

on SerializableSnapshot, minor other cleanup.  Marko Kreen, some further
editorialization by me.

contrib/txid/Makefile

+# $PostgreSQL: pgsql/contrib/txid/Makefile,v 1.2 2007/10/11 19:54:17 tgl Exp $
 
 MODULES = txid
 DATA_built = txid.sql
@@ -5,7 +6,6 @@ DATA = uninstall_txid.sql
 DOCS = README.txid
 REGRESS = txid
 
-
 ifdef USE_PGXS
 PG_CONFIG = pg_config
 PGXS := $(shell $(PG_CONFIG) --pgxs)
@@ -16,11 +16,3 @@ 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/
-

contrib/txid/README.txid

+txid - export transaction IDs to user level
+===========================================
 
-txid - export transaction id's to user level
-============================================
-
-The goal is to make PostgreSQL internal transaction ID and snapshot
+The goal is to make PostgreSQL's internal transaction ID and snapshot
 data usable externally.  This allows very efficient queue
 implementation done inside database.
 
@@ -32,7 +31,7 @@ txid_snapshot_xmax( snap ) returns int8
 txid_snapshot_xip( snap ) setof int8
 
   List of in-progress TXID's in snapshot, that are invisible.
-  Values are between xmin and xmax.
+  Values are between xmin (inclusive) and xmax (exclusive).
 
 txid_visible_in_snapshot(id, snap) returns bool
 
@@ -73,8 +72,8 @@ fetching possible txids below snap1.xmax explicitly:
      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,
+Note that although the above queries work, PostgreSQL fails to
+plan them efficiently.  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.
 
@@ -92,20 +91,16 @@ To see example code for that it's best to see pgq.batch_event_sql() function in
 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;
+When reloading TXID data you will typically want to be sure that the current
+XID counter is beyond the reloaded data.  The easiest way to do this is to
+increase the XID epoch to beyond the largest one in the input data.
 
-So new epoch should be:
+You can look at current epoch with queries such as:
 
-  SELECT (txid_current() >> 32) + 1 as newepoch;
+  SELECT MAX(txid) >> 32 as epoch FROM ...;
 
 Epoch can be changed with pg_resetxlog command:
 
   pg_resetxlog -e NEWEPOCH DATADIR
 
 Database needs to be shut down for that moment.
-
-

contrib/txid/txid.sql.in

@@ -5,21 +5,38 @@
 --
 --	Copyright (c) 2003-2007, PostgreSQL Global Development Group
 --	Author: Jan Wieck, Afilias USA INC.
---
 --	64-bit txids: Marko Kreen, Skype Technologies
+--
+--	$PostgreSQL: pgsql/contrib/txid/txid.sql.in,v 1.2 2007/10/11 19:54:17 tgl Exp $
+--
 -- ----------
 
+-- Adjust this setting to control where the objects get created.
+SET search_path = public;
+
+BEGIN;
+
 --
 -- A special transaction snapshot data type for faster visibility checks
 --
-CREATE OR REPLACE FUNCTION txid_snapshot_in(cstring)
+CREATE TYPE txid_snapshot;
+
+CREATE FUNCTION txid_snapshot_in(cstring)
 	RETURNS txid_snapshot
 	AS 'MODULE_PATHNAME' LANGUAGE C
 	IMMUTABLE STRICT;
-CREATE OR REPLACE FUNCTION txid_snapshot_out(txid_snapshot)
+CREATE FUNCTION txid_snapshot_out(txid_snapshot)
 	RETURNS cstring
 	AS 'MODULE_PATHNAME' LANGUAGE C
 	IMMUTABLE STRICT;
+CREATE FUNCTION txid_snapshot_recv(internal)
+	RETURNS txid_snapshot
+	AS 'MODULE_PATHNAME' LANGUAGE C
+	IMMUTABLE STRICT;
+CREATE FUNCTION txid_snapshot_send(txid_snapshot)
+	RETURNS bytea
+	AS 'MODULE_PATHNAME' LANGUAGE C
+	IMMUTABLE STRICT;
 
 --
 -- The data type itself
@@ -27,42 +44,44 @@ CREATE OR REPLACE FUNCTION txid_snapshot_out(txid_snapshot)
 CREATE TYPE txid_snapshot (
 	INPUT = txid_snapshot_in,
 	OUTPUT = txid_snapshot_out,
+	RECEIVE = txid_snapshot_recv,
+	SEND = txid_snapshot_send,
 	INTERNALLENGTH = variable,
 	STORAGE = extended,
 	ALIGNMENT = double
 );
 
-CREATE OR REPLACE FUNCTION txid_current()
+--
+-- Functions for txid
+--
+CREATE FUNCTION txid_current()
 	RETURNS bigint
 	AS 'MODULE_PATHNAME', 'txid_current' LANGUAGE C
 	STABLE;
 
-CREATE OR REPLACE FUNCTION txid_current_snapshot()
+CREATE 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)
+CREATE 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)
+CREATE 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)
+CREATE 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)
+CREATE FUNCTION txid_visible_in_snapshot(bigint, txid_snapshot)
 	RETURNS boolean
 	AS 'MODULE_PATHNAME', 'txid_visible_in_snapshot' LANGUAGE C
 	IMMUTABLE STRICT;
 
+COMMIT;

contrib/txid/uninstall_txid.sql

-
+SET search_path = public;
 
 DROP FUNCTION txid_current();
 DROP FUNCTION txid_current_snapshot();
@@ -6,10 +6,6 @@ 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);
 
+DROP TYPE txid_snapshot CASCADE;
+-- need cascade to drop the I/O functions