Introduce downgrade scripts for 9.3 versions (#4051)

Here are the updated make targets:
- install: install everything except downgrade scripts.
- install-downgrades: build and install only the downgrade migration scripts.
- install-all: install everything along with the downgrade migration scripts.

(cherry picked from commit 315b323)

This commit is heavily modified to support an earlier release version.
- Downgrade scripts that are relevant for versions 9.4+ are stripped
- multi_extension tests are copied from master and then stripped

Makefile

@@ -24,13 +24,19 @@ install-headers: extension
 	$(INSTALL_DATA) $(citus_top_builddir)/src/include/citus_version.h '$(DESTDIR)$(includedir_server)/'
 # the rest in the source tree
 	$(INSTALL_DATA) $(citus_abs_srcdir)/src/include/distributed/*.h '$(DESTDIR)$(includedir_server)/distributed/'
+
 clean-extension:
 	$(MAKE) -C src/backend/distributed/ clean
 clean-full:
 	$(MAKE) -C src/backend/distributed/ clean-full
 .PHONY: extension install-extension clean-extension clean-full
 # Add to generic targets
 install: install-extension install-headers
+install-downgrades:
+	$(MAKE) -C src/backend/distributed/ install-downgrades
+install-all: install-headers
+	$(MAKE) -C src/backend/distributed/ install-all
+
 clean: clean-extension
 
 # apply or check style
@@ -44,4 +50,4 @@ check-style:
 check: all install
 	$(MAKE) -C src/test/regress check-full
 
-.PHONY: all check install clean
+.PHONY: all check clean install install-downgrades install-all

src/backend/distributed/Makefile

@@ -11,7 +11,9 @@ MODULE_big = citus
 EXTENSION = citus
 
 template_sql_files = $(patsubst $(citus_abs_srcdir)/%,%,$(wildcard $(citus_abs_srcdir)/sql/*.sql))
+template_downgrade_sql_files = $(patsubst $(citus_abs_srcdir)/sql/downgrades/%,%,$(wildcard $(citus_abs_srcdir)/sql/downgrades/*.sql))
 generated_sql_files = $(patsubst %,$(citus_abs_srcdir)/build/%,$(template_sql_files))
+generated_downgrade_sql_files += $(patsubst %,$(citus_abs_srcdir)/build/sql/%,$(template_downgrade_sql_files))
 # All citus--*.sql files that are used to upgrade between versions
 DATA_built = $(generated_sql_files)
 
@@ -54,14 +56,28 @@ SQL_BUILDDIR=build/sql
 
 $(generated_sql_files): $(citus_abs_srcdir)/build/%: %
 	@mkdir -p $(citus_abs_srcdir)/$(SQL_DEPDIR) $(citus_abs_srcdir)/$(SQL_BUILDDIR)
+	@# -MF is used to store dependency files(.Po) in another directory for separation
+	@# -MT is used to change the target of the rule emitted by dependency generation.
+	@# -P is used to inhibit generation of linemarkers in the output from the preprocessor.
+	@# -undef is used to not predefine any system-specific or GCC-specific macros.
+	@# `man cpp` for further information
+	cd $(citus_abs_srcdir) && cpp -undef -w -P -MMD -MP -MF$(SQL_DEPDIR)/$(*F).Po -MT$@ $< > $@
+
+$(generated_downgrade_sql_files): $(citus_abs_srcdir)/build/sql/%: sql/downgrades/%
+	@mkdir -p $(citus_abs_srcdir)/$(SQL_DEPDIR) $(citus_abs_srcdir)/$(SQL_BUILDDIR)
+	@# -MF is used to store dependency files(.Po) in another directory for separation
+	@# -MT is used to change the target of the rule emitted by dependency generation.
+	@# -P is used to inhibit generation of linemarkers in the output from the preprocessor.
+	@# -undef is used to not predefine any system-specific or GCC-specific macros.
+	@# `man cpp` for further information
 	cd $(citus_abs_srcdir) && cpp -undef -w -P -MMD -MP -MF$(SQL_DEPDIR)/$(*F).Po -MT$@ $< > $@
 
 SQL_Po_files := $(wildcard $(SQL_DEPDIR)/*.Po)
 ifneq (,$(SQL_Po_files))
 include $(SQL_Po_files)
 endif
 
-.PHONY: check-sql-snapshots clean-full
+.PHONY: clean-full install install-downgrades install-all
 
 check-sql-snapshots:
 	bash -c '\
@@ -76,6 +92,13 @@ cleanup-before-install:
 
 install: cleanup-before-install
 
+# install and install-downgrades should be run sequentially
+install-all: install
+	make install-downgrades
+
+install-downgrades: $(generated_downgrade_sql_files)
+	$(INSTALL_DATA) $(generated_downgrade_sql_files) '$(DESTDIR)$(datadir)/$(datamoduledir)/'
+
 clean-full:
 	make clean
 	rm -rf $(safestringlib_builddir)

src/backend/distributed/sql/downgrades/citus--9.2-4--9.2-2.sql

@@ -0,0 +1,2 @@
+-- citus--9.2-4--9.2-2
+-- this is an empty downgrade path since citus--9.2-2--9.2-4.sql is empty

src/backend/distributed/sql/downgrades/citus--9.3-2--9.2-4.sql

@@ -0,0 +1,30 @@
+-- citus--9.3-2--9.2-4
+-- this is a downgrade path that will revert the changes made in citus--9.2-4--9.3-2.sql
+--
+-- 9.3-2 added citus extension owner as a distributed object, if not already in there.
+-- However we can not really know if it was a distributed owner prior to 9.3-2.
+-- That's why we leave the record in place.
+
+-- Revert the return type to void
+DROP FUNCTION pg_catalog.citus_extradata_container(INTERNAL);
+CREATE FUNCTION pg_catalog.citus_extradata_container(INTERNAL)
+    RETURNS void
+    LANGUAGE C
+    AS 'MODULE_PATHNAME', $$citus_extradata_container$$;
+COMMENT ON FUNCTION pg_catalog.citus_extradata_container(INTERNAL)
+    IS 'placeholder function to store additional data in postgres node trees';
+
+-- Remove newly introduced functions that are absent in earlier versions
+DROP FUNCTION pg_catalog.update_distributed_table_colocation(regclass, text);
+DROP FUNCTION pg_catalog.replicate_reference_tables();
+DROP FUNCTION pg_catalog.citus_remote_connection_stats(
+    OUT hostname text,
+    OUT port int,
+    OUT database_name text,
+    OUT connection_count_to_node int);
+DROP FUNCTION pg_catalog.worker_create_or_alter_role(
+    role_name text,
+    create_role_utility_query text,
+    alter_role_utility_query text);
+DROP FUNCTION pg_catalog.truncate_local_data_after_distributing_table(
+    function_name regclass);