Introduce logical decoding.

This feature, building on previous commits, allows the write-ahead log
stream to be decoded into a series of logical changes; that is,
inserts, updates, and deletes and the transactions which contain them.
It is capable of handling decoding even across changes to the schema
of the effected tables.  The output format is controlled by a
so-called "output plugin"; an example is included.  To make use of
this in a real replication system, the output plugin will need to be
modified to produce output in the format appropriate to that system,
and to perform filtering.

Currently, information can be extracted from the logical decoding
system only via SQL; future commits will add the ability to stream
changes via walsender.

Andres Freund, with review and other contributions from many other
people, including Álvaro Herrera, Abhijit Menon-Sen, Peter Gheogegan,
Kevin Grittner, Robert Haas, Heikki Linnakangas, Fujii Masao, Abhijit
Menon-Sen, Michael Paquier, Simon Riggs, Craig Ringer, and Steve
Singer.

contrib/Makefile

@@ -50,6 +50,7 @@ SUBDIRS = \
 		spi		\
 		tablefunc	\
 		tcn		\
+		test_decoding	\
 		test_parser	\
 		test_shm_mq	\
 		tsearch2	\

contrib/test_decoding/.gitignore

@@ -0,0 +1,4 @@
+# Generated subdirectories
+/log/
+/results/
+/tmp_check/

contrib/test_decoding/Makefile

@@ -0,0 +1,69 @@
+# contrib/test_decoding/Makefile
+
+MODULES = test_decoding
+OBJS = test_decoding.o
+
+# Note: because we don't tell the Makefile there are any regression tests,
+# we have to clean those result files explicitly
+EXTRA_CLEAN = -r $(pg_regress_clean_files)
+
+ifdef USE_PGXS
+PG_CONFIG = pg_config
+PGXS := $(shell $(PG_CONFIG) --pgxs)
+include $(PGXS)
+else
+subdir = contrib/test_decoding
+top_builddir = ../..
+include $(top_builddir)/src/Makefile.global
+include $(top_srcdir)/contrib/contrib-global.mk
+endif
+
+# Disabled because these tests require "wal_level=logical", which
+# typical installcheck users do not have (e.g. buildfarm clients).
+installcheck:;
+
+# But it can nonetheless be very helpful to run tests on preexisting
+# installation, allow to do so, but only if requested explicitly.
+installcheck-force: regresscheck-install-force isolationcheck-install-force
+
+check: regresscheck isolationcheck
+
+submake-regress:
+	$(MAKE) -C $(top_builddir)/src/test/regress all
+
+submake-isolation:
+	$(MAKE) -C $(top_builddir)/src/test/isolation all
+
+submake-test_decoding:
+	$(MAKE) -C $(top_builddir)/contrib/test_decoding
+
+REGRESSCHECKS=ddl rewrite toast permissions decoding_in_xact binary
+
+regresscheck: all | submake-regress submake-test_decoding
+	$(pg_regress_check) \
+	    --temp-config $(top_srcdir)/contrib/test_decoding/logical.conf \
+	    --temp-install=./tmp_check \
+	    --extra-install=contrib/test_decoding \
+	    $(REGRESSCHECKS)
+
+regresscheck-install-force: | submake-regress submake-test_decoding
+	$(pg_regress_installcheck) \
+	    --extra-install=contrib/test_decoding \
+	    $(REGRESSCHECKS)
+
+ISOLATIONCHECKS=mxact delayed_startup concurrent_ddl_dml
+
+isolationcheck: all | submake-isolation submake-test_decoding
+	$(pg_isolation_regress_check) \
+	    --temp-config $(top_srcdir)/contrib/test_decoding/logical.conf \
+	    --extra-install=contrib/test_decoding \
+	    $(ISOLATIONCHECKS)
+
+isolationcheck-install-force: all | submake-isolation submake-test_decoding
+	$(pg_isolation_regress_installcheck) \
+	    --extra-install=contrib/test_decoding \
+	    $(ISOLATIONCHECKS)
+
+PHONY: submake-test_decoding submake-regress check \
+	regresscheck regresscheck-install-force \
+	isolationcheck isolationcheck-install-force

contrib/test_decoding/expected/binary.out

@@ -0,0 +1,35 @@
+-- predictability
+SET synchronous_commit = on;
+SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
+ ?column? 
+----------
+ init
+(1 row)
+
+-- succeeds, textual plugin, textual consumer
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'force-binary', '0');
+ data 
+------
+(0 rows)
+
+-- fails, binary plugin, textual consumer
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'force-binary', '1');
+ERROR:  output plugin cannot produce text output
+-- succeeds, textual plugin, binary consumer
+SELECT data FROM pg_logical_slot_get_binary_changes('regression_slot', NULL, NULL, 'force-binary', '0');
+ data 
+------
+(0 rows)
+
+-- succeeds, binary plugin, binary consumer
+SELECT data FROM pg_logical_slot_get_binary_changes('regression_slot', NULL, NULL, 'force-binary', '1');
+ data 
+------
+(0 rows)
+
+SELECT 'init' FROM pg_drop_replication_slot('regression_slot');
+ ?column? 
+----------
+ init
+(1 row)
+