Remove unused XLogAODropSegmentFile function

The XLogAODropSegmentFile function was used for implementing invalid
page logging for AO.  In the past year, there have been significant
changes after removing MMXLOG_REMOVE_FILE XLOG record type that make
this function no longer needed (currently only being used by a unit
test).  The most relevant change is that deletion of AO segment files
only happen during DROP TABLE (vacuum was changed to truncate the
segment file) which makes things easier for AO to reuse the existing
invalid page logging implementation.

References:
https://github.com/greenplum-db/gpdb/commit/175c25e8fb0494933087ff19ef29d7377e021702
https://github.com/greenplum-db/gpdb/commit/8165e1b1627b9b2f8b40c3c55eab9de3d137b70a
https://github.com/greenplum-db/gpdb/commit/8838ac983c66af74d0a1422337cf92f08fbe5f2c

src/backend/access/transam/test/Makefile

@@ -4,8 +4,6 @@ include $(top_builddir)/src/Makefile.global
 
 TARGETS=xact distributedlog xlog varsup
 
-TARGETS += xlogutils
-
 include $(top_builddir)/src/backend/mock.mk
 
 distributedlog.t: \

src/backend/access/transam/test/xlogutils_test.c

-#include <stdarg.h>
-#include <stddef.h>
-#include <setjmp.h>
-#include "cmockery.h"
-
-#include "../xlogutils.c"
-
-#include "catalog/pg_tablespace.h"
-
-/*
- * Test that the invalid_page_tab hash table is properly used when invalid AO
- * segment files are encountered.
- */
-void
-test_ao_invalid_segment_file(void **state)
-{
-	RelFileNode relfilenode;
-	int32 segmentFileNum;
-
-	/* create mock relfilenode */
-	relfilenode.spcNode = DEFAULTTABLESPACE_OID;
-	relfilenode.dbNode = 12087 /* postgres database */;
-	relfilenode.relNode = FirstNormalObjectId;
-
-	segmentFileNum = 2;
-
-	/* invalid_page_tab should not be initialized */
-	assert_true(invalid_page_tab == NULL);
-
-	/* initialize invalid_page_tab and log an invalid AO segment file */
-	XLogAOSegmentFile(relfilenode, segmentFileNum);
-	assert_false(invalid_page_tab == NULL);
-	assert_int_equal(hash_get_num_entries(invalid_page_tab), 1);
-
-	/* try again but should not put in same entry */
-	XLogAOSegmentFile(relfilenode, segmentFileNum);
-	assert_int_equal(hash_get_num_entries(invalid_page_tab), 1);
-
-	/* forget the invalid AO segment file */
-	XLogAODropSegmentFile(relfilenode, segmentFileNum);
-	assert_int_equal(hash_get_num_entries(invalid_page_tab), 0);
-}
-
-int
-main(int argc, char* argv[])
-{
-	cmockery_parse_arguments(argc, argv);
-
-	const UnitTest tests[] = {
-		unit_test(test_ao_invalid_segment_file)
-	};
-	return run_tests(tests);
-}

src/backend/access/transam/xlogutils.c

@@ -203,31 +203,6 @@ forget_invalid_pages_db(Oid dbid)
 	}
 }
 
-/* Forget an invalid AO/AOCO segment file */
-static void
-forget_invalid_segment_file(RelFileNode rnode, uint32 segmentFileNum)
-{
-	xl_invalid_page_key key;
-	bool		found;
-
-	if (invalid_page_tab == NULL)
-		return;					/* nothing to do */
-
-	key.node = rnode;
-	key.forkno = MAIN_FORKNUM;
-	key.blkno = segmentFileNum;
-	hash_search(invalid_page_tab,
-				(void *) &key,
-				HASH_FIND, &found);
-	if (!found)
-		return;
-
-	if (hash_search(invalid_page_tab,
-					(void *) &key,
-					HASH_REMOVE, &found) == NULL)
-		elog(ERROR, "hash table corrupted");
-}
-
 /* Are there any unresolved references to invalid pages? */
 bool
 XLogHaveInvalidPages(void)
@@ -411,10 +386,12 @@ XLogReadBufferExtended(RelFileNode rnode, ForkNumber forknum,
 
 /*
  * If the AO segment file does not exist, log the relfilenode into the
- * invalid_page_table hash table using the segment file number as the
- * block number to avoid creating a new hash table.  The entry will be
- * removed if there is a following MMXLOG_REMOVE_FILE record for the
- * relfilenode.
+ * invalid_page_table hash table using the segment file number as the block
+ * number to avoid creating a new hash table specifically for AO.  The entry
+ * will be removed if there is a following xlog redo commit prepared record
+ * for deleting the relfilenode.  The segment file number here is only used
+ * for a debug message since XLogDropRelation logic will remove all
+ * invalid_page_tab entries that have the same relfilenode and fork number.
  */
 void
 XLogAOSegmentFile(RelFileNode rnode, uint32 segmentFileNum)
@@ -508,13 +485,6 @@ XLogDropRelation(RelFileNode rnode, ForkNumber forknum)
 	forget_invalid_pages(rnode, forknum, 0);
 }
 
-/* Drop an AO/CO segment file from the invalid_page_tab hash table */
-void
-XLogAODropSegmentFile(RelFileNode rnode, uint32 segmentFileNum)
-{
-	forget_invalid_segment_file(rnode, segmentFileNum);
-}
-
 /*
  * Drop a whole database during XLOG replay
  *

src/include/access/xlogutils.h

@@ -30,6 +30,5 @@ extern Relation CreateFakeRelcacheEntry(RelFileNode rnode);
 extern void FreeFakeRelcacheEntry(Relation fakerel);
 
 extern void XLogAOSegmentFile(RelFileNode rnode, uint32 segmentFileNum);
-extern void XLogAODropSegmentFile(RelFileNode rnode, uint32 segmentFileNum);
 
 #endif