Add very basic infrastructure for schema upgrade scripts.

Citus' extension version now has a -$schemaversion appendix.  When the
schema is changed, a new schema version has to be added; changes to the
same schema version several commits inside a single pull request are ok.

Schema migration scripts between each schema version have to be
added. To ensure upgrade scripts work correctly a new regression test
ensures that all steps work.

The extension scripts to-be-used for CREATE EXTENSION (i.e. not
extension updates) are generated by concatenating citus.sql and the
relevant migration scripts.

src/backend/distributed/Makefile

@@ -5,8 +5,11 @@ citus_top_builddir = ../../..
 
 MODULE_big = citus
 EXTENSION = citus
-EXTVERSION = 5.0
-DATA_built = $(EXTENSION)--$(EXTVERSION).sql
+EXTVERSIONS = 5.0 5.0-1
+# All citus--*.sql files in the source directory
+DATA = $(patsubst $(citus_abs_srcdir)/%.sql,%.sql,$(wildcard $(citus_abs_srcdir)/$(EXTENSION)--*--*.sql))
+# Generated files for each version
+DATA_built = $(foreach v,$(EXTVERSIONS),$(EXTENSION)--$(v).sql)
 SCRIPTS = ../../bin/scripts/copy_to_distributed_table
 
 # directories with source files
@@ -20,8 +23,11 @@ OBJS += \
 # be explicit about the default target
 all:
 
-# define build process for latest install file
-$(EXTENSION)--$(EXTVERSION).sql: $(EXTENSION).sql
+# generate each version's file installation file by concatenating
+# previous upgrade scripts
+$(EXTENSION)--5.0.sql: $(EXTENSION).sql
+	cat $^ > $@
+$(EXTENSION)--5.0-1.sql: $(EXTENSION)--5.0.sql $(EXTENSION)--5.0--5.0-1.sql
 	cat $^ > $@
 
 NO_PGXS = 1

src/backend/distributed/citus--5.0--5.0-1.sql

@@ -0,0 +1,3 @@
+/* citus--5.0--5.0-1.sql */
+
+-- Currently nothing to do here

src/backend/distributed/citus.control

@@ -1,6 +1,6 @@
 # Citus extension
 comment = 'Citus distributed database'
-default_version = '5.0'
+default_version = '5.0-1'
 module_pathname = '$libdir/citus'
 relocatable = false
 schema = pg_catalog

src/test/regress/expected/multi_extension.out

@@ -0,0 +1,17 @@
+--
+-- MULTI_EXTENSION
+--
+-- Tests around extension creation / upgrades
+--
+-- It'd be nice to script generation of this file, but alas, that's
+-- not done yet.
+-- DROP EXTENSION pre-created by the regression suite
+DROP EXTENSION citus;
+\c
+-- Create extension in oldest version, test every upgrade step
+CREATE EXTENSION citus VERSION '5.0';
+ALTER EXTENSION citus UPDATE TO '5.0-1';
+-- drop extension an re-create in newest version
+DROP EXTENSION citus;
+\c
+CREATE EXTENSION citus;

src/test/regress/multi_schedule

@@ -11,6 +11,7 @@
 # ---
 # Tests around schema changes, these are run first, so there's no preexisting objects.
 # ---
+test: multi_extension
 test: multi_table_ddl
 
 # ----------

src/test/regress/sql/multi_extension.sql

@@ -0,0 +1,20 @@
+--
+-- MULTI_EXTENSION
+--
+-- Tests around extension creation / upgrades
+--
+-- It'd be nice to script generation of this file, but alas, that's
+-- not done yet.
+
+-- DROP EXTENSION pre-created by the regression suite
+DROP EXTENSION citus;
+\c
+
+-- Create extension in oldest version, test every upgrade step
+CREATE EXTENSION citus VERSION '5.0';
+ALTER EXTENSION citus UPDATE TO '5.0-1';
+
+-- drop extension an re-create in newest version
+DROP EXTENSION citus;
+\c
+CREATE EXTENSION citus;