From ea9950a145fa47bbf55d46aafa6e4ae890b8bf6f Mon Sep 17 00:00:00 2001
From: Narayanan Iyer <nars@yottadb.com>
Date: Fri, 7 Jul 2023 17:03:00 -0400
Subject: [PATCH] [YDBTest#501] [DEBUG-ONLY] ydb_test_4g_db_blks env var allows
 creation of databases with > 4Gib blocks

Background
----------
* GT.M V7.0-000 added support for up to 16Gi blocks in a region (see YDBTest#501 for details).

* Once the block number goes more than 4Gi, it becomes an 8-byte value. So GT.M had to change
  all usages of 4-byte block numbers in the code base (using `block_id` type) to 8-byte values.

* YDBTest#501 had to test this change. But testing it was not straightforward as more than 4GiB
  blocks meant creating a 2 terabyte file even with the smallest block size of 512 bytes. With a
  default block size of 4KiB, it meant creating an 8 terabyte file. Although such huge files are
  sparse, the database structure implied a bitmap block every 512 blocks which meant the database
  file in the file system will be a huge file where only 1 in every 512 block is allocated. But
  even such a file would end up taking a lot of space and take a lot of time to create making it
  very difficult to run the entire suite of YDBTest tests with such huge database files.

Solution
--------
* Below is pasted from https://gitlab.com/YottaDB/DB/YDBTest/-/issues/501#note_1468633286.

  For the record. This is an idea to test block numbers greater than 4GiB (i.e. where the higher order
  4-byte is non-zero) without the overhead of test runtime due to creating bitmaps (which happen every
  512 blocks) in the database file.

  A debug-build only env var `ydb_test_4g_db_blks` will be honored by YottaDB. If this var is undefined
  or set to 0, then there is no change. But if this is set to a non-zero value, it indicates the size of
  the HOLE in the database starting from local bitmap number `1` (i.e. database block number `512`). Any
  database block (including bitmap blocks) in the range from block 512 to the bitmap block number specified
  by the env var will not be allocated/used by the database logic. This way we force the database logic
  to allocate blocks past the HOLE effectively getting into 8-byte block number territory without actually
  allocating HUGE files in the file system. The created database file will be a giant sparse file.

* If this env var is set to the value `8388608`, the size of the database file with a default block size
  of 4KiB would be 16TiB (16 terabytes) and the database would support 4GiB blocks.

Implementation
--------------
* The value of the env var `ydb_test_4g_db_blks` is stored in the debug-only global variable `ydb_skip_bml_num`
  (defined in `sr_port/gbldefs.c`). This happens in `sr_port/gtm_env_init.c`.

  Since this is a new env var, there is a new line in `sr_port/ydb_logicals_tab.h`.

* The YDBTest test system framework will be changed separately to run all existing tests with this env var
  set to the value `8388608`.

* Various files had to be modified in this commit to ensure the database code does not use any block
  in the range from local bitmap block `512` upto (but not including) the local bitmap block number
  specified by `$ydb_test_4g_db_blks * 512` thus creating a big HOLE in the database file after block `511`.

* Below is a high level list of the changes that happened.
  - MUPIP CREATE and MUPIP EXTEND create the HOLE as appropriate (mucregini.c, mu_cre_file.c, mu_int_maps.c,
    gdsfilext.c and gdsfilext_nojnl.c). They accurately maintains `total_blks` and `free_blks` even when
    there is a HOLE. Blocks in the HOLE are counted towards both these counters.
  - `bm_getfree.c` ensures any newly allocated blocks are not in the HOLE.
  - The following commands skip/honor/ignore the HOLE.
    - MUPIP REORG UPGRADE/DOWNGRADE (`sr_port/mu_reorg_upgrd_dwngrd.c`)
    - MUPIP REORG (in `mu_swap_blk.c` and `sr_unix/mu_swap_root.c`)
    - MUPIP REORG -TRUNCATE (`sr_unix/mu_truncate.c`)
    - MUPIP INTEG (in `sr_unix/mu_int_init.c`, `sr_port/mu_int_maps.c` and `sr_port/mupip_integ.c`)
    - MUPIP RESTORE (in `sr_unix/mupip_restore.c`)
    - DSE MAPS (in `sr_port/dse_maps.c`)
    - MUPIP BACKUP -INCREMENTAL (in `sr_unix/mubinccpy.c`)
    - DSE RANGE (in `sr_port/dse_range.c`)
  - DB_LSEEKREAD (in `sr_unix/gtmio.h`) and DB_LSEEKWRITE (in `sr_port/anticipatory_freeze.h`) macros now
    have asserts to ensure we never read/write any block in the HOLE. One exception was that the function
    `db_write_eof_block()` writes data at the end of the database file which could end up being in the HOLE
    in case the database has blocks 0 to 511 allocated presently. Therefore the asserts were avoided in that
    case by temporarily resetting `ydb_skip_bml_num` to 0.
  - `dsk_read.c` needed to handle read of a block in the HOLE region (possible due to concurrency issues).
  - `warn_db_sz.c` needed to not issue a LOWSPC warning when huge db files are in use. Or else one would
    see test failures due to these extra messages whenever the env var is randomly enabled by the tests.

Bugs identified
---------------
* Below was a pre-existing GT.M V7.0-000 code issue I noticed after the changes in this commit.
  The `mu_int_blks_to_upgrd` global variable counted the number of blocks but was typed as `int4`.
  It should have been changed to `block_id`. This got missed out in GT.M V7.0-000. And is fixed in this
  commit. Interestingly, the same fix happened on the GT.M side in V7.1-000.

* Additionally, I noticed a few missing 4-byte to 8-byte conversions thanks to the changes in the above bullets.
  They are the following and are fixed in this commit to use `block_id` instead of `int4`/`uint4`.
  - `freeblks` local variable in `sr_port/mur_process_intrpt_recov.c`
  - `i` and `fcnt` local variables in `sr_port/mur_blocks_free.c`
  - Return value of `mur_blocks_free()` (which returns the number of free blocks and hence should be 8-byte)
---
 sr_port/anticipatory_freeze.h      | 11 ++++++++-
 sr_port/bm_getfree.c               | 31 ++++++++++++++++++++++++
 sr_port/dse_maps.c                 | 14 +++++++++++
 sr_port/dse_range.c                | 11 +++++++++
 sr_port/gbldefs.c                  |  3 +++
 sr_port/gtm_env_init.c             | 18 +++++++++++++-
 sr_port/mu_int_blk.c               |  2 +-
 sr_port/mu_int_init.c              | 12 ++++++++-
 sr_port/mu_int_maps.c              | 12 +++++++--
 sr_port/mu_reorg_upgrd_dwngrd.c    | 13 +++++++++-
 sr_port/mu_swap_blk.c              | 14 +++++++++++
 sr_port/mucregini.c                | 15 +++++++++++-
 sr_port/mupip_integ.c              |  9 ++++++-
 sr_port/muprec.h                   |  4 +--
 sr_port/mur_blocks_free.c          | 21 +++++++++++++---
 sr_port/mur_process_intrpt_recov.c |  5 ++--
 sr_port/ydb_logicals_tab.h         |  3 ++-
 sr_unix/db_write_eof_block.c       | 21 ++++++++++++++++
 sr_unix/dsk_read.c                 | 16 ++++++++++++
 sr_unix/gdsfilext.c                | 39 +++++++++++++++++++++++++++++-
 sr_unix/gdsfilext_nojnl.c          | 11 ++++++++-
 sr_unix/gtmio.h                    | 19 +++++++++++----
 sr_unix/mu_cre_file.c              |  8 +++++-
 sr_unix/mu_swap_root.c             | 15 ++++++++++++
 sr_unix/mu_truncate.c              |  6 ++++-
 sr_unix/mubinccpy.c                | 13 +++++++++-
 sr_unix/mupip_restore.c            | 20 ++++++++++++++-
 sr_unix/warn_db_sz.c               | 11 +++++++++
 28 files changed, 349 insertions(+), 28 deletions(-)

diff --git a/sr_port/anticipatory_freeze.h b/sr_port/anticipatory_freeze.h
index 6b297b0c7..f929a0a9a 100644
--- a/sr_port/anticipatory_freeze.h
+++ b/sr_port/anticipatory_freeze.h
@@ -3,7 +3,7 @@
  * Copyright (c) 2012-2020 Fidelity National Information	*
  * Services, Inc. and/or its subsidiaries. All rights reserved.	*
  *								*
- * Copyright (c) 2018-2020 YottaDB LLC and/or its subsidiaries.	*
+ * Copyright (c) 2018-2023 YottaDB LLC and/or its subsidiaries.	*
  * All rights reserved.						*
  *								*
  *	This source code contains the intellectual property	*
@@ -335,6 +335,10 @@ MBSTART {															\
 #define DB_LSEEKWRITE_HANG(CSA)	FALSE
 #endif
 
+#ifdef DEBUG
+GBLREF	gtm_int8	ydb_skip_bml_num;	/* Use "gtm_int8" since it is possible "block_id" type is not yet defined */
+#endif
+
 /* #GTM_THREAD_SAFE : The below macro (DB_LSEEKWRITE) is thread-safe */
 #define	DB_LSEEKWRITE(CSA, UDI, DB_FN, FD, OFFSET, BUFF, SIZE, STATUS)							\
 MBSTART {														\
@@ -344,6 +348,11 @@ MBSTART {														\
 	assert(!CSA_LOCAL || !CSA_LOCAL->region || FILE_INFO(CSA_LOCAL->region)->grabbed_access_sem			\
 			|| !(CSA_LOCAL)->nl || !FROZEN_CHILLED(CSA_LOCAL) || FREEZE_LATCH_HELD(CSA_LOCAL));		\
 	DBG_CHECK_DIO_ALIGNMENT(UDI, OFFSET, BUFF, SIZE);								\
+	assert((0 == ydb_skip_bml_num) || (NULL == UDI) || (0 == OFFSET)						\
+		|| ((BLK_ZERO_OFF(((unix_db_info *)UDI)->s_addrs.hdr->start_vbn)					\
+			+ ((gtm_int8)BLKS_PER_LMAP * ((unix_db_info *)UDI)->s_addrs.hdr->blk_size)) > OFFSET)		\
+		|| ((BLK_ZERO_OFF(((unix_db_info *)UDI)->s_addrs.hdr->start_vbn)					\
+			+ (ydb_skip_bml_num * ((unix_db_info *)UDI)->s_addrs.hdr->blk_size)) <= OFFSET));		\
 	/* We should never write to a READ_ONLY db file header unless we hold standalone access on the db */		\
 	assert((0 != OFFSET) || !((sgmnt_data_ptr_t)BUFF)->read_only || (NULL == UDI) || UDI->grabbed_access_sem);	\
 	DO_LSEEKWRITE(CSA_LOCAL, DB_FN, FD, OFFSET, BUFF, SIZE, STATUS, fake_db_enospc, DB_LSEEKWRITE_HANG(CSA),	\
diff --git a/sr_port/bm_getfree.c b/sr_port/bm_getfree.c
index 84300d41c..4268f48c5 100644
--- a/sr_port/bm_getfree.c
+++ b/sr_port/bm_getfree.c
@@ -70,6 +70,10 @@ GBLREF uint4		dollar_tlevel;
 GBLREF uint4		update_array_size, cumul_update_array_size;
 GBLREF unsigned int	t_tries;
 
+#ifdef DEBUG
+GBLREF	block_id	ydb_skip_bml_num;
+#endif
+
 error_def(ERR_DBBADFREEBLKCTR);
 error_def(ERR_DBMBMINCFREFIXED);
 
@@ -89,6 +93,10 @@ block_id bm_getfree(block_id hint, boolean_t *blk_used, unsigned int cw_work, cw
 	total_blks = (dba_mm == cs_data->acc_meth) ? cs_addrs->total_blks : cs_addrs->ti->total_blks;
 	if (hint >= total_blks)		/* for TP, hint can be > total_blks */
 		hint = 1;
+#	ifdef DEBUG
+	if ((0 != ydb_skip_bml_num) && (BLKS_PER_LMAP <= hint) && (hint < ydb_skip_bml_num))
+		hint = ydb_skip_bml_num;
+#	endif
 	hint_cycled = DIVIDE_ROUND_UP(total_blks, BLKS_PER_LMAP);
 	hint_limit = DIVIDE_ROUND_DOWN(hint, BLKS_PER_LMAP);
 	local_maps = hint_cycled + 2;	/* for (up to) 2 wraps */
@@ -102,6 +110,10 @@ block_id bm_getfree(block_id hint, boolean_t *blk_used, unsigned int cw_work, cw
 			{
 				hint_cycled = hint_limit;
 				hint = 1;
+#				ifdef DEBUG
+				if ((0 != ydb_skip_bml_num) && (BLKS_PER_LMAP <= hint) && (hint < ydb_skip_bml_num))
+					hint = ydb_skip_bml_num;
+#				endif
 				continue;
 			}
 			if (SS_NORMAL != (status = GDSFILEXT(cs_data->extension_size, total_blks, TRANS_IN_PROG_TRUE)))
@@ -125,6 +137,13 @@ block_id bm_getfree(block_id hint, boolean_t *blk_used, unsigned int cw_work, cw
 			continue;
 		}
 		bml *= BLKS_PER_LMAP;
+#		ifdef DEBUG
+		if ((0 != ydb_skip_bml_num) && (BLKS_PER_LMAP <= bml) && (bml < ydb_skip_bml_num))
+		{
+			hint = ydb_skip_bml_num + 1;
+			continue;
+		}
+#		endif
 		if (ROUND_DOWN2(hint, BLKS_PER_LMAP) != bml)
 		{	/* not within requested map */
 			if ((bml < hint) && (hint_cycled))	/* wrap? - second one should force an extend for sure */
@@ -271,6 +290,17 @@ boolean_t	is_free_blks_ctr_ok(void)
 	local_maps = DIVIDE_ROUND_UP(total_blks, BLKS_PER_LMAP);
 	for (free_blocks = 0, free_bml = 0; free_bml < local_maps; free_bml++)
 	{
+#		ifdef DEBUG
+		if ((0 != ydb_skip_bml_num)
+			&& (BLKS_PER_LMAP <= (BLKS_PER_LMAP * free_bml))
+			&& ((BLKS_PER_LMAP * free_bml) < ydb_skip_bml_num))
+		{
+			free_bml = (ydb_skip_bml_num / BLKS_PER_LMAP) - 1;
+				/* - 1 to compensate the "free_bml++" done in "for" loop line */
+			free_blocks += (ydb_skip_bml_num - BLKS_PER_LMAP) / BLKS_PER_LMAP * (BLKS_PER_LMAP - 1);
+			continue;
+		}
+#		endif
 		bml = bmm_find_free((uint4)free_bml, (sm_uc_ptr_t)MM_ADDR(cs_data), local_maps);
 		if (bml < free_bml)
 			break;
@@ -299,6 +329,7 @@ boolean_t	is_free_blks_ctr_ok(void)
 	assert(cs_addrs->ti->free_blocks == free_blocks);
 	if (cs_addrs->ti->free_blocks != free_blocks)
 	{
+		assert(FALSE);
 		send_msg_csa(CSA_ARG(cs_addrs) VARLSTCNT(6) ERR_DBBADFREEBLKCTR, 4, DB_LEN_STR(gv_cur_region),
 				&(cs_addrs->ti->free_blocks), &free_blocks);
 		cs_addrs->ti->free_blocks = free_blocks;
diff --git a/sr_port/dse_maps.c b/sr_port/dse_maps.c
index 91bb55806..5234afa21 100644
--- a/sr_port/dse_maps.c
+++ b/sr_port/dse_maps.c
@@ -3,6 +3,9 @@
  * Copyright (c) 2001-2021 Fidelity National Information	*
  * Services, Inc. and/or its subsidiaries. All rights reserved.	*
  *								*
+ * Copyright (c) 2023 YottaDB LLC and/or its subsidiaries.	*
+ * All rights reserved.						*
+ *								*
  *	This source code contains the intellectual property	*
  *	of its copyright holder(s), and is made available	*
  *	under a license.  If you do not know the terms of	*
@@ -56,6 +59,10 @@ GBLREF short		crash_count;
 GBLREF srch_hist	dummy_hist;
 GBLREF uint4		update_array_size;
 
+#ifdef DEBUG
+GBLREF	block_id		ydb_skip_bml_num;
+#endif
+
 error_def(ERR_DBRDONLY);
 error_def(ERR_DSEBLKRDFAIL);
 error_def(ERR_DSEFAIL);
@@ -120,6 +127,13 @@ void dse_maps(void)
 		dse_m_rest(blk, bml_list, bml_size, &csa->ti->free_blocks, TRUE);
 		for (blk_index = 0, bml_index = 0;  blk_index < total_blks; blk_index += bplmap, bml_index++)
 		{
+#			ifdef DEBUG
+			if ((0 != ydb_skip_bml_num) && (BLKS_PER_LMAP == blk_index))
+			{
+				bml_index += (ydb_skip_bml_num - blk_index) / BLKS_PER_LMAP;
+				blk_index = ydb_skip_bml_num;
+			}
+#			endif
 			t_begin_crit(ERR_DSEFAIL);
 			CHECK_TN(csa, csd, csd->trans_hist.curr_tn);	/* can issue rts_error TNTOOLARGE */
 			CWS_RESET;
diff --git a/sr_port/dse_range.c b/sr_port/dse_range.c
index 32d88f5c2..75abfd771 100644
--- a/sr_port/dse_range.c
+++ b/sr_port/dse_range.c
@@ -41,6 +41,10 @@ GBLREF short int	patch_path_count;
 GBLREF sgmnt_addrs	*cs_addrs;
 GBLREF VSIG_ATOMIC_T	util_interrupt;
 
+#ifdef DEBUG
+GBLREF	block_id	ydb_skip_bml_num;
+#endif
+
 error_def(ERR_CTRLC);
 error_def(ERR_DSEBLKRDFAIL);
 error_def(ERR_DSEINVALBLKID);
@@ -103,6 +107,13 @@ void dse_range(void)
 	DSE_GRAB_CRIT_AS_APPROPRIATE(was_crit, was_hold_onto_crit, nocrit_present, cs_addrs, gv_cur_region);
 	for (blk = from; blk <= to ;blk++)
 	{
+#		ifdef DEBUG
+		if ((0 != ydb_skip_bml_num) && (BLKS_PER_LMAP <= blk) && (blk < ydb_skip_bml_num))
+		{
+			blk = ydb_skip_bml_num - 1;
+			continue;
+		}
+#		endif
 		if (util_interrupt)
 		{
 			DSE_REL_CRIT_AS_APPROPRIATE(was_crit, was_hold_onto_crit, nocrit_present, cs_addrs, gv_cur_region);
diff --git a/sr_port/gbldefs.c b/sr_port/gbldefs.c
index 8d158c6ad..3559912ae 100644
--- a/sr_port/gbldefs.c
+++ b/sr_port/gbldefs.c
@@ -1419,3 +1419,6 @@ GBLDEF	boolean_t	ydb_treat_sigusr2_like_sigusr1;	/* set based on env var "ydb_tr
 GBLDEF	int		jobinterrupt_sig_num;		/* Set to signal number that caused $ZINTERRUPT (SIGUSR1/SIGUSR2).
 							 * Used to derive the value of the ISV $ZYINTRSIG.
 							 */
+#ifdef DEBUG
+GBLDEF	block_id	ydb_skip_bml_num;	/* See comment in "sr_port/gtm_env_init.c" for purpose */
+#endif
diff --git a/sr_port/gtm_env_init.c b/sr_port/gtm_env_init.c
index bbb4d8ab4..fc61e67c3 100644
--- a/sr_port/gtm_env_init.c
+++ b/sr_port/gtm_env_init.c
@@ -3,7 +3,7 @@
  * Copyright (c) 2004-2020 Fidelity National Information	*
  * Services, Inc. and/or its subsidiaries. All rights reserved.	*
  *								*
- * Copyright (c) 2017-2022 YottaDB LLC and/or its subsidiaries. *
+ * Copyright (c) 2017-2023 YottaDB LLC and/or its subsidiaries. *
  * All rights reserved.						*
  *								*
  *	This source code contains the intellectual property	*
@@ -87,6 +87,10 @@ GBLREF	int		ydb_repl_filter_timeout;/* # of seconds that source server waits bef
 GBLREF  boolean_t 	dollar_test_default; 	/* Default value taken by dollar_truth via dollar_test_default */
 GBLREF	boolean_t	gtm_nofflf;		/* Used to control "write #" behavior ref GTM-9136 */
 
+#ifdef DEBUG
+GBLREF	block_id	ydb_skip_bml_num;
+#endif
+
 void	gtm_env_init(void)
 {
 	boolean_t		ret, is_defined;
@@ -223,6 +227,18 @@ void	gtm_env_init(void)
 		ret = ydb_logical_truth_value(YDBENVINDX_DIRTREE_COLLHDR_ALWAYS, FALSE, &is_defined);
 		if (is_defined)
 			TREF(ydb_dirtree_collhdr_always) = ret; /* if logical is not defined, the TREF takes the default value */
+		/* ydb_test_4g_db_blks env var. If set to a non-zero value of N, it implies blocks from the 1st local bitmap
+		 * to the N-1th local bitmap block are not allocated in the db file. After the 0th local bitmap block, the
+		 * Nth local bitmap block is where block allocation continues. This helps test records in the database blocks
+		 * that contain 8-byte block numbers where the higher order 4-byte is non-zero. This effectively tests all
+		 * code (mostly added in GT.M V7.0-000 and merged into YottaDB r2.00) that handles 8-byte block numbers.
+		 * A 0 value implies this scheme is disabled.
+		 */
+		ydb_skip_bml_num = (block_id)ydb_trans_numeric(YDBENVINDX_TEST_4G_DB_BLKS, &is_defined, IGNORE_ERRORS_TRUE, NULL);
+		if (!is_defined)
+			ydb_skip_bml_num = 0;
+		else
+			ydb_skip_bml_num *= BLKS_PER_LMAP;
 #		endif
 		/* GDS Block certification */
 		ret = ydb_logical_truth_value(YDBENVINDX_GDSCERT, FALSE, &is_defined);
diff --git a/sr_port/mu_int_blk.c b/sr_port/mu_int_blk.c
index b321b291d..65287b54c 100644
--- a/sr_port/mu_int_blk.c
+++ b/sr_port/mu_int_blk.c
@@ -147,7 +147,7 @@ GBLREF gtm_uint64_t		mu_int_cum[CUM_TYPE_MAX][MAX_BT_DEPTH + 1];
 GBLREF uint4			mu_int_offset[];
 GBLREF uint4			mu_int_errknt;
 GBLREF block_id			mu_int_path[];
-GBLREF int4			mu_int_blks_to_upgrd;
+GBLREF block_id			mu_int_blks_to_upgrd;
 GBLREF global_list		*trees;
 GBLREF global_list		*trees_tail;
 GBLREF gv_key			*mu_end_key;
diff --git a/sr_port/mu_int_init.c b/sr_port/mu_int_init.c
index 3d7d041aa..188bfc241 100644
--- a/sr_port/mu_int_init.c
+++ b/sr_port/mu_int_init.c
@@ -3,7 +3,7 @@
  * Copyright (c) 2001-2018 Fidelity National Information	*
  * Services, Inc. and/or its subsidiaries. All rights reserved.	*
  *								*
- * Copyright (c) 2019-2022 YottaDB LLC and/or its subsidiaries.	*
+ * Copyright (c) 2019-2023 YottaDB LLC and/or its subsidiaries.	*
  * All rights reserved.						*
  *								*
  *	This source code contains the intellectual property	*
@@ -91,6 +91,11 @@ boolean_t mu_int_init(void)
 	fc->op = FC_READ;
 	/* Do aligned reads if opened with O_DIRECT */
 	udi = FC2UDI(fc);
+#	ifdef DEBUG
+	udi->s_addrs.hdr = NULL;	/* Clear previous value of udi->s_addrs.hdr as it would have been freed up
+					 * inside STANDALONE macro invoked above.
+					 */
+#	endif
 	tsd = udi->fd_opened_with_o_direct ? (sgmnt_data_ptr_t)(TREF(dio_buff)).aligned : &mu_int_data;
 	fc->op_buff = (uchar_ptr_t)tsd;
 	fc->op_len = SGMNT_HDR_LEN;
@@ -99,6 +104,11 @@ boolean_t mu_int_init(void)
 	/* Ensure "mu_int_data" is populated even if we did not directly read into it for the O_DIRECT case */
 	if (udi->fd_opened_with_o_direct)
 		memcpy(&mu_int_data, (TREF(dio_buff)).aligned, SGMNT_HDR_LEN);
+#	ifdef DEBUG
+	udi->s_addrs.hdr = &mu_int_data;	/* Now that we have read in the file header, point udi to it for the next dbfilop.
+						 * This is used by the DB_LSEEKREAD macro if "ydb_skip_bml_num" is non-zero.
+						 */
+#	endif
 	if (MASTER_MAP_SIZE_MAX < MASTER_MAP_SIZE(&mu_int_data) ||
 	    native_size < DIVIDE_ROUND_UP(SGMNT_HDR_LEN + MASTER_MAP_SIZE(&mu_int_data), DISK_BLOCK_SIZE) + MIN_DB_BLOCKS)
 	{
diff --git a/sr_port/mu_int_maps.c b/sr_port/mu_int_maps.c
index 15dc1412a..adf524263 100644
--- a/sr_port/mu_int_maps.c
+++ b/sr_port/mu_int_maps.c
@@ -3,7 +3,7 @@
  * Copyright (c) 2001-2020 Fidelity National Information	*
  * Services, Inc. and/or its subsidiaries. All rights reserved.	*
  *								*
- * Copyright (c) 2022 YottaDB LLC and/or its subsidiaries.	*
+ * Copyright (c) 2022-2023 YottaDB LLC and/or its subsidiaries.	*
  * All rights reserved.						*
  *								*
  *	This source code contains the intellectual property	*
@@ -43,7 +43,7 @@ GBLREF	sgmnt_data		mu_int_data;
 GBLREF	block_id		mu_int_path[];
 GBLREF	boolean_t		tn_reset_this_reg;
 GBLREF	int			mu_int_plen;
-GBLREF	int4			mu_int_blks_to_upgrd;
+GBLREF	block_id		mu_int_blks_to_upgrd;
 GBLREF	int			disp_map_errors;
 GBLREF	int			mu_map_errs;
 GBLREF	int			disp_trans_errors;
@@ -54,6 +54,10 @@ GBLREF	sgmnt_addrs		*cs_addrs;
 
 GBLREF trans_num	largest_tn;
 
+#ifdef DEBUG
+GBLREF	block_id		ydb_skip_bml_num;
+#endif
+
 error_def(ERR_DBREADBM);
 error_def(ERR_DBLVLINC);
 error_def(ERR_DBMBSIZMN);
@@ -119,6 +123,10 @@ void mu_int_maps(void)
 	{
 		assert(mapsize == mu_int_data.bplmap);
 		blkno = mcnt * mu_int_data.bplmap;
+#		ifdef DEBUG
+		if ((0 != ydb_skip_bml_num) && (0 < blkno) && (blkno < ydb_skip_bml_num))
+			continue;
+#		endif
 		bml_busy(0, mu_int_locals + ((blkno * BML_BITS_PER_BLK) / BITS_PER_UCHAR));
 		blk_base = mu_int_read(blkno, &ondsk_blkver, &free_blk_base);	/* ondsk_blkver set to GDSV4 or GDSV6 (GDSVCURR) */
 		if (!blk_base)
diff --git a/sr_port/mu_reorg_upgrd_dwngrd.c b/sr_port/mu_reorg_upgrd_dwngrd.c
index 36bae5663..ee8f57e23 100644
--- a/sr_port/mu_reorg_upgrd_dwngrd.c
+++ b/sr_port/mu_reorg_upgrd_dwngrd.c
@@ -3,7 +3,7 @@
  * Copyright (c) 2005-2021 Fidelity National Information	*
  * Services, Inc. and/or its subsidiaries. All rights reserved.	*
  *								*
- * Copyright (c) 2018-2020 YottaDB LLC and/or its subsidiaries.	*
+ * Copyright (c) 2018-2023 YottaDB LLC and/or its subsidiaries.	*
  * All rights reserved.						*
  *								*
  *	This source code contains the intellectual property	*
@@ -89,6 +89,10 @@ GBLREF	unsigned char		cw_set_depth;
 GBLREF	unsigned char		cw_map_depth;
 GBLREF	uint4			update_trans;
 
+#ifdef DEBUG
+GBLREF	block_id		ydb_skip_bml_num;
+#endif
+
 error_def(ERR_BUFFLUFAILED);
 error_def(ERR_DBBTUWRNG);
 error_def(ERR_DBFILERR);
@@ -328,6 +332,13 @@ void	mu_reorg_upgrd_dwngrd(void)
 		memset(&reorg_stats, 0, SIZEOF(reorg_stats));	/* initialize statistics for this region */
 		for (curbmp = start_bmp; curbmp <= last_bmp; curbmp += BLKS_PER_LMAP)
 		{
+#			ifdef DEBUG
+			if ((0 != ydb_skip_bml_num) && (BLKS_PER_LMAP <= curbmp) && (curbmp < ydb_skip_bml_num))
+			{
+				curbmp = ydb_skip_bml_num - BLKS_PER_LMAP;
+				continue;
+			}
+#			endif
 			if (mu_ctrly_occurred || mu_ctrlc_occurred)
 			{
 				status1 = ERR_MUNOFINISH;
diff --git a/sr_port/mu_swap_blk.c b/sr_port/mu_swap_blk.c
index fd9c718f6..692802545 100644
--- a/sr_port/mu_swap_blk.c
+++ b/sr_port/mu_swap_blk.c
@@ -3,6 +3,9 @@
  * Copyright (c) 2001-2020 Fidelity National Information	*
  * Services, Inc. and/or its subsidiaries. All rights reserved.	*
  *								*
+ * Copyright (c) 2023 YottaDB LLC and/or its subsidiaries.	*
+ * All rights reserved.						*
+ *								*
  *	This source code contains the intellectual property	*
  *	of its copyright holder(s), and is made available	*
  *	under a license.  If you do not know the terms of	*
@@ -79,6 +82,10 @@ GBLREF unsigned int	t_tries;
 GBLREF gv_key		*gv_currkey;
 GBLREF hash_table_int8	cw_stagnate;
 
+#ifdef DEBUG
+GBLREF	block_id	ydb_skip_bml_num;
+#endif
+
 /******************************************************************************************
 Input Parameters:
 	level: level of working block
@@ -147,6 +154,13 @@ enum cdb_sc mu_swap_blk(int level, block_id *pdest_blk_id, kill_set *kill_set_pt
 	{
 		blk_was_free = FALSE;
 		INCR_BLK_NUM(dest_blk_id);
+#		ifdef DEBUG
+		if ((0 != ydb_skip_bml_num) && (BLKS_PER_LMAP < dest_blk_id) && (dest_blk_id < ydb_skip_bml_num))
+		{
+			dest_blk_id = ydb_skip_bml_num;
+			continue;
+		}
+#		endif
 		/* A Pre-order traversal should not cause a child block to go to its parent.
 		 * However, in case it happens because already the organization was like that or for any other reason, skip swap.
 		 * If we decide to swap, code below should be changed to take care of the special case.
diff --git a/sr_port/mucregini.c b/sr_port/mucregini.c
index edcfe3e32..08008dbc3 100644
--- a/sr_port/mucregini.c
+++ b/sr_port/mucregini.c
@@ -3,7 +3,7 @@
  * Copyright (c) 2001-2020 Fidelity National Information	*
  * Services, Inc. and/or its subsidiaries. All rights reserved.	*
  *								*
- * Copyright (c) 2019 YottaDB LLC and/or its subsidiaries.	*
+ * Copyright (c) 2019-2023 YottaDB LLC and/or its subsidiaries.	*
  * All rights reserved.						*
  *								*
  *	This source code contains the intellectual property	*
@@ -68,6 +68,10 @@ GBLREF 	sgmnt_data_ptr_t	cs_data;
 GBLREF 	sgmnt_addrs		*cs_addrs;
 GBLREF	void			(*mupip_exit_fp)(int4 errnum);
 
+#ifdef DEBUG
+GBLREF	block_id		ydb_skip_bml_num;
+#endif
+
 error_def(ERR_COLLATIONUNDEF);
 error_def(ERR_COLLTYPVERSION);
 error_def(ERR_DBFILERR);
@@ -266,6 +270,11 @@ void mucregini(block_id blk_init_size)
 	NUM_CRIT_ENTRY(csd) = seg->mutex_slots;
 	csd->wcs_phase2_commit_wait_spincnt = WCS_PHASE2_COMMIT_DEFAULT_SPINCNT;
 	csd->defer_allocate = seg->defer_allocate;
+#	ifdef DEBUG
+	/* Force-enable DEFER_ALLOCATE in case ydb_skip_bml_num is non-zero to avoid huge test runtimes */
+	if (0 != ydb_skip_bml_num)
+		csd->defer_allocate = TRUE;
+#	endif
 	csd->read_only = seg->read_only;
 	time(&ctime);
 	assert(SIZEOF(ctime) >= SIZEOF(int4));
@@ -283,6 +292,10 @@ void mucregini(block_id blk_init_size)
 	bmm_init();
 	for (i = 0; i < blk_init_size ; i += csd->bplmap)
 	{
+#		ifdef DEBUG
+		if ((0 != ydb_skip_bml_num) && (0 < i) && (i < ydb_skip_bml_num))
+			i = ydb_skip_bml_num;
+#		endif
 		status = bml_init(i);
 		if (status != SS_NORMAL)
 		{
diff --git a/sr_port/mupip_integ.c b/sr_port/mupip_integ.c
index b64b1f721..803d26520 100644
--- a/sr_port/mupip_integ.c
+++ b/sr_port/mupip_integ.c
@@ -117,7 +117,7 @@ GBLDEF global_list		*trees;
 GBLDEF sgmnt_data		mu_int_data;
 GBLDEF unsigned char		*mu_int_master;
 GBLDEF trans_num		largest_tn;
-GBLDEF int4			mu_int_blks_to_upgrd;
+GBLDEF block_id			mu_int_blks_to_upgrd;
 GBLDEF span_node_integ		*sndata;
 GBLDEF boolean_t		null_coll_type_err = FALSE;
 GBLDEF boolean_t		null_coll_type;
@@ -442,6 +442,13 @@ void mupip_integ(void)
 			 * verifications
 			 */
 			csd = &mu_int_data;
+#			ifdef DEBUG
+			fc = gv_cur_region->dyn.addr->file_cntl;
+			udi = FC2UDI(fc);
+			udi->s_addrs.hdr = csd;	/* Needed by asserts in "DB_LSEEKREAD" macro in "dbfilop()" calls when
+						 * "ydb_skip_bml_num" is non-zero.
+						 */
+#			endif
 		}
 		trees_tail = trees = (global_list *)malloc(SIZEOF(global_list));
 		memset(trees, 0, SIZEOF(global_list));
diff --git a/sr_port/muprec.h b/sr_port/muprec.h
index 65e90034a..8924d1197 100644
--- a/sr_port/muprec.h
+++ b/sr_port/muprec.h
@@ -3,7 +3,7 @@
  * Copyright (c) 2001-2020 Fidelity National Information	*
  * Services, Inc. and/or its subsidiaries. All rights reserved.	*
  *								*
- * Copyright (c) 2018-2021 YottaDB LLC and/or its subsidiaries.	*
+ * Copyright (c) 2018-2023 YottaDB LLC and/or its subsidiaries.	*
  * All rights reserved.						*
  *								*
  *	This source code contains the intellectual property	*
@@ -1282,7 +1282,7 @@ uint4			mur_back_phase1(reg_ctl_list *rctl);
 uint4			mur_back_phase2(reg_ctl_list *rctl);
 uint4			mur_back_processing_one_region(mur_back_opt_t *mur_back_options);
 int4 			mur_block_count_correct(reg_ctl_list *rctl);
-int4			mur_blocks_free(reg_ctl_list *rctl);
+block_id		mur_blocks_free(reg_ctl_list *rctl);
 boolean_t		mur_close_files(void);
 int4			mur_cre_file_extfmt(jnl_ctl_list *jctl, int recstat);
 void			mur_close_file_extfmt(boolean_t in_mur_close_files);
diff --git a/sr_port/mur_blocks_free.c b/sr_port/mur_blocks_free.c
index c86446003..bb4dbc896 100644
--- a/sr_port/mur_blocks_free.c
+++ b/sr_port/mur_blocks_free.c
@@ -3,6 +3,9 @@
  * Copyright (c) 2001-2021 Fidelity National Information	*
  * Services, Inc. and/or its subsidiaries. All rights reserved.	*
  *								*
+ * Copyright (c) 2023 YottaDB LLC and/or its subsidiaries.	*
+ * All rights reserved.						*
+ *								*
  *	This source code contains the intellectual property	*
  *	of its copyright holder(s), and is made available	*
  *	under a license.  If you do not know the terms of	*
@@ -38,16 +41,20 @@
 GBLREF	gd_region		*gv_cur_region;
 GBLREF	sgmnt_data_ptr_t	cs_data;
 
+#ifdef DEBUG
+GBLREF	block_id	ydb_skip_bml_num;
+#endif
+
 #define BPL	SIZEOF(int4)*8/BML_BITS_PER_BLK					/* blocks masked by a int4 */
 
 error_def(ERR_DBRDERR);
 error_def(ERR_DYNUPGRDFAIL);
 
-int4 mur_blocks_free(reg_ctl_list *rctl)
+block_id mur_blocks_free(reg_ctl_list *rctl)
 {
 	int4		x;
-	block_id	bnum, maps;
-	int		mapsize, i, j, k, fcnt, status;
+	block_id	bnum, maps, i, fcnt;
+	int		mapsize, j, k, status;
 	unsigned char	*c, *disk, *m_ptr;
 	uint4		*dskmap, map_blk_size;
 	file_control	*db_ctl;
@@ -75,6 +82,14 @@ int4 mur_blocks_free(reg_ctl_list *rctl)
 	db_ctl->op_len = cs_data->blk_size;
 	for (i = 0; i != maps; i++)
 	{
+#		ifdef DEBUG
+		if ((0 != ydb_skip_bml_num) && (1 == i))
+		{
+			i = ydb_skip_bml_num / BLKS_PER_LMAP - 1;
+			fcnt += (ydb_skip_bml_num - BLKS_PER_LMAP) / BLKS_PER_LMAP * (BLKS_PER_LMAP - 1);
+			continue;
+		}
+#		endif
 		bnum = i * cs_data->bplmap;
 		db_ctl->op = FC_READ;
 		db_ctl->op_pos = cs_data->start_vbn + ((gtm_int64_t)cs_data->blk_size / DISK_BLOCK_SIZE * bnum);
diff --git a/sr_port/mur_process_intrpt_recov.c b/sr_port/mur_process_intrpt_recov.c
index 43f82083b..0eaef7065 100644
--- a/sr_port/mur_process_intrpt_recov.c
+++ b/sr_port/mur_process_intrpt_recov.c
@@ -3,7 +3,7 @@
  * Copyright (c) 2003-2017 Fidelity National Information	*
  * Services, Inc. and/or its subsidiaries. All rights reserved.	*
  *								*
- * Copyright (c) 2018 YottaDB LLC and/or its subsidiaries.	*
+ * Copyright (c) 2018-2023 YottaDB LLC and/or its subsidiaries.	*
  * All rights reserved.						*
  *								*
  *	This source code contains the intellectual property	*
@@ -63,7 +63,8 @@ uint4 mur_process_intrpt_recov()
 	char				prev_jnl_fn[MAX_FN_LEN + 1], rename_fn[MAX_FN_LEN + 1];
 	jnl_create_info			jnl_info;
 	uint4				status, status2;
-	uint4				max_autoswitchlimit, max_jnl_alq, max_jnl_deq, freeblks;
+	uint4				max_autoswitchlimit, max_jnl_alq, max_jnl_deq;
+	block_id			freeblks;
 	sgmnt_addrs			*csa;
 	sgmnt_data_ptr_t		csd;
 	jnl_private_control		*jpc;
diff --git a/sr_port/ydb_logicals_tab.h b/sr_port/ydb_logicals_tab.h
index 3060c70c0..e3452f08b 100644
--- a/sr_port/ydb_logicals_tab.h
+++ b/sr_port/ydb_logicals_tab.h
@@ -1,6 +1,6 @@
 /****************************************************************
  *								*
- * Copyright (c) 2018-2022 YottaDB LLC and/or its subsidiaries.	*
+ * Copyright (c) 2018-2023 YottaDB LLC and/or its subsidiaries.	*
  * All rights reserved.						*
  *								*
  *	This source code contains the intellectual property	*
@@ -178,6 +178,7 @@ YDBENVINDX_TABLE_ENTRY (YDBENVINDX_DB_COUNTER_SEM_INCR,        "$ydb_db_counter_
 YDBENVINDX_TABLE_ENTRY (YDBENVINDX_DIRTREE_COLLHDR_ALWAYS,     "$ydb_dirtree_collhdr_always",     "$gtm_dirtree_collhdr_always")
 YDBENVINDX_TABLE_ENTRY (YDBENVINDX_GVUNDEF_FATAL,              "$ydb_gvundef_fatal",              "$gtm_gvundef_fatal")
 YDBENVINDX_TABLE_ENTRY (YDBENVINDX_LOCKHASH_N_BITS,            "$ydb_lockhash_n_bits",            "")
+YDBENVINDX_TABLE_ENTRY (YDBENVINDX_TEST_4G_DB_BLKS,            "$ydb_test_4g_db_blks",            "")
 YDBENVINDX_TABLE_ENTRY (YDBENVINDX_TEST_AUTORELINK_ALWAYS,     "$ydb_test_autorelink_always",     "$gtm_test_autorelink_always")
 YDBENVINDX_TABLE_ENTRY (YDBENVINDX_TEST_FAKE_ENOSPC,           "$ydb_test_fake_enospc",           "$gtm_test_fake_enospc")
 YDBENVINDX_TABLE_ENTRY (YDBENVINDX_TEST_JNLPOOL_SYNC,          "$ydb_test_jnlpool_sync",          "$gtm_test_jnlpool_sync")
diff --git a/sr_unix/db_write_eof_block.c b/sr_unix/db_write_eof_block.c
index 1e5c56e23..000317d72 100644
--- a/sr_unix/db_write_eof_block.c
+++ b/sr_unix/db_write_eof_block.c
@@ -3,6 +3,9 @@
  * Copyright (c) 2016 Fidelity National Information		*
  * Services, Inc. and/or its subsidiaries. All rights reserved.	*
  *								*
+ * Copyright (c) 2023 YottaDB LLC and/or its subsidiaries.	*
+ * All rights reserved.						*
+ *								*
  *	This source code contains the intellectual property	*
  *	of its copyright holder(s), and is made available	*
  *	under a license.  If you do not know the terms of	*
@@ -25,6 +28,10 @@
 #include "gtmio.h"
 #include "anticipatory_freeze.h"
 
+#ifdef DEBUG
+GBLREF	block_id	ydb_skip_bml_num;
+#endif
+
 /* #GTM_THREAD_SAFE : The below function db_write_eof_block is thread-safe */
 int	db_write_eof_block(unix_db_info *udi, int fd, int blk_size, off_t offset, dio_buff_t *diobuff)
 {
@@ -48,7 +55,21 @@ int	db_write_eof_block(unix_db_info *udi, int fd, int blk_size, off_t offset, di
 	{
 		csa = &udi->s_addrs;
 		assert(fd == udi->fd);
+#		ifdef DEBUG
+		block_id	save_ydb_skip_bml_num;
+
+		/* It is possible we write an EOF block to the offset corresponding to bitmap block BLKS_PER_LMAP. In that case,
+		 * we want to disable the "ydb_skip_bml_num" related assert in DB_LSEEKWRITE. We do that by resetting
+		 * "ydb_skip_bml_num" to 0 in that case.
+		 */
+		save_ydb_skip_bml_num = ydb_skip_bml_num;
+		if (offset == (BLK_ZERO_OFF(udi->s_addrs.hdr->start_vbn) + (BLKS_PER_LMAP * udi->s_addrs.hdr->blk_size)))
+			ydb_skip_bml_num = 0;
+#		endif
 		DB_LSEEKWRITE(csa, udi, udi->fn, fd, offset, buff, blk_size, status);
+#		ifdef DEBUG
+		ydb_skip_bml_num = save_ydb_skip_bml_num;	/* restore "ydb_skip_bml_num" in case it got reset */
+#		endif
 	} else
 		DB_LSEEKWRITE(NULL, ((unix_db_info *)NULL), NULL, fd, offset, buff, blk_size, status);
 	if (free_needed)
diff --git a/sr_unix/dsk_read.c b/sr_unix/dsk_read.c
index 5f78dc326..b620a1b52 100644
--- a/sr_unix/dsk_read.c
+++ b/sr_unix/dsk_read.c
@@ -65,6 +65,10 @@ GBLREF	jnl_gbls_t		jgbl;
 GBLREF	uint4			process_id;
 GBLREF	uint4			mu_reorg_encrypt_in_prog;
 
+#ifdef DEBUG
+GBLREF	block_id		ydb_skip_bml_num;
+#endif
+
 error_def(ERR_DYNUPGRDFAIL);
 
 int4	dsk_read (block_id blk, sm_uc_ptr_t buff, enum db_ver *ondsk_blkver, boolean_t blk_free)
@@ -121,6 +125,18 @@ int4	dsk_read (block_id blk, sm_uc_ptr_t buff, enum db_ver *ondsk_blkver, boolea
 	assert(csd == cs_data);
 	size = csd->blk_size;
 	assert(csd->acc_meth == dba_bg);
+#	ifdef DEBUG
+	if ((0 != ydb_skip_bml_num) && (BLKS_PER_LMAP <= blk) && (blk < ydb_skip_bml_num))
+	{	/* Huge db scheme is in effect and a block in the range of the HOLE in the huge db (any block
+		 * number from the bitmap block BLKS_PER_LMAP to block "ydb_skip_bml_num-1") was specified. This is possible
+		 * in case of a restartable transaction situation. In this case, just return a zeroed block and the
+		 * transaction will eventually restart.
+		 */
+		memset(buff, 0, size);
+		in_dsk_read--;
+		return 0;
+	}
+#	endif
 	/* Since csd->fully_upgraded is referenced more than once in this module (once explicitly and once in
 	 * GDS_BLK_UPGRADE_IF_NEEDED macro used below), take a copy of it and use that so all usages see the same value.
 	 * Not doing this, for example, can cause us to see the database as fully upgraded in the first check causing us
diff --git a/sr_unix/gdsfilext.c b/sr_unix/gdsfilext.c
index 942b0496b..4950c9574 100644
--- a/sr_unix/gdsfilext.c
+++ b/sr_unix/gdsfilext.c
@@ -81,7 +81,15 @@ MBSTART {															\
 			2, LEN_AND_LIT("Please make more disk space available or shutdown GT.M to avoid data loss"), ENOSPC);	\
 } MBEND
 
-#define SUSPICIOUS_EXTEND 	(2 * (dollar_tlevel ? sgm_info_ptr->cw_set_depth : cw_set_depth) < cs_addrs->ti->free_blocks)
+#ifdef DEBUG
+GBLREF	block_id	ydb_skip_bml_num;
+#endif
+
+#define SUSPICIOUS_EXTEND 	((2 * (dollar_tlevel ? sgm_info_ptr->cw_set_depth : cw_set_depth)				\
+					DEBUG_ONLY( + ((0 != ydb_skip_bml_num)							\
+						? ((ydb_skip_bml_num - BLKS_PER_LMAP) / BLKS_PER_LMAP * (BLKS_PER_LMAP - 1))	\
+						: 0)))										\
+					< cs_addrs->ti->free_blocks)								\
 
 GBLREF	sigset_t		blockalrm;
 GBLREF	sgmnt_addrs		*cs_addrs;
@@ -100,6 +108,10 @@ GBLREF	boolean_t		ydb_dbfilext_syslog_disable;	/* control whether db file extens
 GBLREF	uint4			ydbDebugLevel;
 GBLREF	jnlpool_addrs_ptr_t	jnlpool;
 
+#ifdef DEBUG
+GBLREF	block_id		ydb_skip_bml_num;
+#endif
+
 error_def(ERR_DBFILERR);
 error_def(ERR_DBFILEXT);
 error_def(ERR_DSKSPACEFLOW);
@@ -183,6 +195,14 @@ int4 gdsfilext(block_id blocks, block_id filesize, boolean_t trans_in_prog)
 			- DIVIDE_ROUND_UP(cs_data->trans_hist.total_blks, bplmap) + blocks, bplmap - 1)
 			- DIVIDE_ROUND_UP(cs_data->trans_hist.total_blks, bplmap);
 	new_blocks = blocks + new_bit_maps;
+#	ifdef DEBUG
+	if ((0 != ydb_skip_bml_num) && (BLKS_PER_LMAP >= cs_data->trans_hist.total_blks)
+			&& (BLKS_PER_LMAP < (cs_data->trans_hist.total_blks + new_blocks)))
+	{
+		new_blocks += (ydb_skip_bml_num - BLKS_PER_LMAP);
+		new_bit_maps += (ydb_skip_bml_num - BLKS_PER_LMAP) / BLKS_PER_LMAP;
+	}
+#	endif
 	assert((0 < new_blocks) || (!cs_data->defer_allocate && (0 == new_blocks)));
 	if (new_blocks + cs_data->trans_hist.total_blks > MAXTOTALBLKS(cs_data))
 	{
@@ -196,6 +216,10 @@ int4 gdsfilext(block_id blocks, block_id filesize, boolean_t trans_in_prog)
 		RTS_ERROR_CSA_ABT(cs_addrs, VARLSTCNT(5) ERR_DBFILERR, 2, DB_LEN_STR(gv_cur_region), save_errno);
 	} else
 	{
+#		ifdef DEBUG
+		if (0 == ydb_skip_bml_num)
+		{
+#		endif
 		if (!(ydbDebugLevel & GDL_IgnoreAvailSpace))
 		{	/* Bypass this space check if debug flag above is on. Allows us to create a large sparce DB
 			 * in space it could never fit it if wasn't sparse. Needed for some tests.
@@ -218,6 +242,9 @@ int4 gdsfilext(block_id blocks, block_id filesize, boolean_t trans_in_prog)
 				}
 			}
 		}
+#		ifdef DEBUG
+		}
+#		endif
 	}
 #	ifdef DEBUG
 	if ( (WBTEST_ENABLED(WBTEST_MM_CONCURRENT_FILE_EXTEND) && dollar_tlevel && !MEMCMP_LIT(gv_cur_region->rname, "DEFAULT")) ||
@@ -482,6 +509,11 @@ int4 gdsfilext(block_id blocks, block_id filesize, boolean_t trans_in_prog)
 		for (map = ROUND_UP(old_total, bplmap); map < new_total; map += bplmap)
 		{
 			DEBUG_ONLY(new_bit_maps--;)
+#			ifdef DEBUG
+			assert(0 < map);
+			if ((0 != ydb_skip_bml_num) && (map < ydb_skip_bml_num))
+				continue;
+#			endif
 			if (SS_NORMAL != (status = bml_init(map)))
 			{
 				GDSFILEXT_CLNUP;
@@ -519,6 +551,11 @@ int4 gdsfilext(block_id blocks, block_id filesize, boolean_t trans_in_prog)
 	assert(cs_data->blks_to_upgrd == (inctn_detail.blks2upgrd_struct.blks_to_upgrd_delta + prev_extend_blks_to_upgrd));
 	assert((0 < blocks) || (!cs_data->defer_allocate && (0 == new_blocks)));
 	assert(0 < (cs_addrs->ti->free_blocks + blocks));
+#	ifdef DEBUG
+	if ((0 != ydb_skip_bml_num) && (BLKS_PER_LMAP >= cs_data->trans_hist.total_blks)
+				&& (BLKS_PER_LMAP < (cs_data->trans_hist.total_blks + new_blocks)))
+		blocks += (ydb_skip_bml_num - BLKS_PER_LMAP) / BLKS_PER_LMAP * (BLKS_PER_LMAP - 1);
+#	endif
 	cs_addrs->ti->free_blocks += blocks;
 	cs_addrs->total_blks = cs_addrs->ti->total_blks = new_total;
 	blocks = old_total;
diff --git a/sr_unix/gdsfilext_nojnl.c b/sr_unix/gdsfilext_nojnl.c
index 2abb309d3..f3acc8ecd 100644
--- a/sr_unix/gdsfilext_nojnl.c
+++ b/sr_unix/gdsfilext_nojnl.c
@@ -3,7 +3,7 @@
  * Copyright (c) 2012-2020 Fidelity National Information	*
  * Services, Inc. and/or its subsidiaries. All rights reserved.	*
  *								*
- * Copyright (c) 2019 YottaDB LLC and/or its subsidiaries.	*
+ * Copyright (c) 2019-2023 YottaDB LLC and/or its subsidiaries.	*
  * All rights reserved.						*
  *								*
  *	This source code contains the intellectual property	*
@@ -62,6 +62,10 @@
 
 GBLREF	jnl_gbls_t	jgbl;
 
+#ifdef DEBUG
+GBLREF	block_id	ydb_skip_bml_num;
+#endif
+
 error_def(ERR_DBFILERR);
 
 /* Minimal file extend. Called (at the moment) from mur_back_process.c when processing JRT_TRUNC record.
@@ -126,6 +130,11 @@ int gdsfilext_nojnl(gd_region* reg, block_id new_total, block_id old_total)
 	/* initialize bitmaps, if any new ones are added */
 	for (ii = ROUND_UP(old_total, BLKS_PER_LMAP); ii < new_total; ii += BLKS_PER_LMAP)
 	{
+#		ifdef DEBUG
+		assert(0 < ii);
+		if ((0 != ydb_skip_bml_num) && (ii < ydb_skip_bml_num))
+			continue;
+#		endif
 		offset = (off_t)BLK_ZERO_OFF(csd->start_vbn) + (off_t)ii * blk_size;
 		DB_LSEEKWRITE(csa, udi, udi->fn, udi->fd, offset, aligned_buff, blk_size, status);
 		if (0 != status)
diff --git a/sr_unix/gtmio.h b/sr_unix/gtmio.h
index a5b3d4c4a..1101e8174 100644
--- a/sr_unix/gtmio.h
+++ b/sr_unix/gtmio.h
@@ -3,7 +3,7 @@
  * Copyright (c) 2001-2018 Fidelity National Information	*
  * Services, Inc. and/or its subsidiaries. All rights reserved.	*
  *								*
- * Copyright (c) 2018-2021 YottaDB LLC and/or its subsidiaries.	*
+ * Copyright (c) 2018-2023 YottaDB LLC and/or its subsidiaries.	*
  * All rights reserved.						*
  *								*
  *	This source code contains the intellectual property	*
@@ -384,10 +384,19 @@ MBSTART {											\
 		RC = -1;		/* Something kept us from reading what we wanted */	\
 } MBEND
 
-#define	DB_LSEEKREAD(UDI, FD, OFFSET, BUFF, SIZE, STATUS)		\
-MBSTART {								\
-	DBG_CHECK_DIO_ALIGNMENT(UDI, OFFSET, BUFF, SIZE);		\
-	LSEEKREAD(FD, OFFSET, BUFF, SIZE, STATUS);			\
+#ifdef DEBUG
+GBLREF	gtm_int8	ydb_skip_bml_num;	/* Use "gtm_int8" since it is possible "block_id" type is not yet defined */
+#endif
+
+#define	DB_LSEEKREAD(UDI, FD, OFFSET, BUFF, SIZE, STATUS)							\
+MBSTART {													\
+	DBG_CHECK_DIO_ALIGNMENT(UDI, OFFSET, BUFF, SIZE);							\
+	assert((0 == ydb_skip_bml_num) || (0 == OFFSET) || (NULL == ((unix_db_info *)UDI)->s_addrs.hdr)		\
+		|| ((BLK_ZERO_OFF(((unix_db_info *)UDI)->s_addrs.hdr->start_vbn)				\
+			+ ((gtm_int8)BLKS_PER_LMAP * ((unix_db_info *)UDI)->s_addrs.hdr->blk_size)) > OFFSET)	\
+		|| ((BLK_ZERO_OFF(((unix_db_info *)UDI)->s_addrs.hdr->start_vbn)				\
+			+ (ydb_skip_bml_num * ((unix_db_info *)UDI)->s_addrs.hdr->blk_size)) <= OFFSET));	\
+	LSEEKREAD(FD, OFFSET, BUFF, SIZE, STATUS);					\
 } MBEND
 
 /* The below macro is almost the same as LSEEKREAD except it has an extra parameter where the number of
diff --git a/sr_unix/mu_cre_file.c b/sr_unix/mu_cre_file.c
index 25cefdc24..31eb1a12f 100644
--- a/sr_unix/mu_cre_file.c
+++ b/sr_unix/mu_cre_file.c
@@ -3,7 +3,7 @@
  * Copyright (c) 2001-2021 Fidelity National Information	*
  * Services, Inc. and/or its subsidiaries. All rights reserved.	*
  *								*
- * Copyright (c) 2018-2022 YottaDB LLC and/or its subsidiaries.	*
+ * Copyright (c) 2018-2023 YottaDB LLC and/or its subsidiaries.	*
  * All rights reserved.						*
  *								*
  *	This source code contains the intellectual property	*
@@ -128,6 +128,7 @@ GBLREF	sgmnt_data_ptr_t	cs_data;
 GBLREF	uint4			ydbDebugLevel;
 #ifdef DEBUG
 GBLREF	boolean_t		in_mu_cre_file;
+GBLREF	block_id		ydb_skip_bml_num;
 #endif
 
 STATICDEF	int	mu_cre_file_fd;		/* needed for "mu_cre_file_ch" */
@@ -403,6 +404,10 @@ unsigned char mu_cre_file(boolean_t caller_is_mupip_create)
 	 * manner as every non-bitmap block must have an associated bitmap)
 	 */
 	cs_data->trans_hist.total_blks += DIVIDE_ROUND_UP(cs_data->trans_hist.total_blks, BLKS_PER_LMAP - 1);
+#	ifdef DEBUG
+	if ((0 != ydb_skip_bml_num) && (BLKS_PER_LMAP < cs_data->trans_hist.total_blks))
+		cs_data->trans_hist.total_blks += (ydb_skip_bml_num - BLKS_PER_LMAP);
+#	endif
 	cs_data->extension_size = gv_cur_region->dyn.addr->ext_blk_count;
 	/* Check if this file is an encrypted database. If yes, do init */
 	if (IS_ENCRYPTED(gv_cur_region->dyn.addr->is_encrypted))
@@ -454,6 +459,7 @@ unsigned char mu_cre_file(boolean_t caller_is_mupip_create)
 	}
 	if (!cs_data->defer_allocate)
 	{
+		assert(0 == ydb_skip_bml_num);
 		status = posix_fallocate(udi->fd, 0, BLK_ZERO_OFF(cs_data->start_vbn) +
 					 ((off_t)(cs_data->trans_hist.total_blks + 1) * cs_data->blk_size));
 		if (0 != status)
diff --git a/sr_unix/mu_swap_root.c b/sr_unix/mu_swap_root.c
index 60c1ff4f2..d78ae1f81 100644
--- a/sr_unix/mu_swap_root.c
+++ b/sr_unix/mu_swap_root.c
@@ -79,6 +79,10 @@ GBLREF	unsigned char		cw_set_depth;
 GBLREF	unsigned char		rdfail_detail;
 GBLREF	unsigned int		t_tries;
 
+#ifdef DEBUG
+GBLREF	block_id		ydb_skip_bml_num;
+#endif
+
 #define RETRY_SWAP		(0)
 #define ABORT_SWAP		(1)
 
@@ -306,6 +310,17 @@ block_id swap_root_or_directory_block(int parent_blk_lvl, int child_blk_lvl, src
 		t_abort(gv_cur_region, csa);
 		return ABORT_SWAP;
 	}
+#	ifdef DEBUG
+	if ((0 != ydb_skip_bml_num) && (1 == master_bit))
+	{
+		master_bit = bmm_find_free(ydb_skip_bml_num / BLKS_PER_LMAP, csa->bmm, num_local_maps);
+		if ((NO_FREE_SPACE == master_bit) || (1 == master_bit))
+		{
+			t_abort(gv_cur_region, csa);
+			return ABORT_SWAP;
+		}
+	}
+#	endif
 	bmlhist.blk_num = master_bit * BLKS_PER_LMAP;
 	if (NULL == (bmlhist.buffaddr = t_qread(bmlhist.blk_num, (sm_int_ptr_t)&bmlhist.cycle, &bmlhist.cr)))
 	{
diff --git a/sr_unix/mu_truncate.c b/sr_unix/mu_truncate.c
index 187f226f4..9582aefb3 100644
--- a/sr_unix/mu_truncate.c
+++ b/sr_unix/mu_truncate.c
@@ -3,7 +3,7 @@
  * Copyright (c) 2012-2021 Fidelity National Information	*
  * Services, Inc. and/or its subsidiaries. All rights reserved.	*
  *								*
- * Copyright (c) 2019-2022 YottaDB LLC and/or its subsidiaries.	*
+ * Copyright (c) 2019-2023 YottaDB LLC and/or its subsidiaries.	*
  * All rights reserved.						*
  *								*
  *	This source code contains the intellectual property	*
@@ -213,6 +213,10 @@ boolean_t mu_truncate(int4 truncate_percent, mval *keep_mval)
 			return TRUE;
 		}
 		lmap_blk_num = lmap_num * BLKS_PER_LMAP;
+#		ifdef DEBUG
+		if ((0 != ydb_skip_bml_num) && (BLKS_PER_LMAP <= lmap_blk_num) && (lmap_blk_num < ydb_skip_bml_num))
+			break;
+#		endif
 		if (csa->nl->highest_lbm_with_busy_blk >= lmap_blk_num)
 		{
 			found_busy_blk = lmap_blk_num;
diff --git a/sr_unix/mubinccpy.c b/sr_unix/mubinccpy.c
index 610f11aac..fa29e9c57 100644
--- a/sr_unix/mubinccpy.c
+++ b/sr_unix/mubinccpy.c
@@ -3,7 +3,7 @@
  * Copyright (c) 2001-2020 Fidelity National Information	*
  * Services, Inc. and/or its subsidiaries. All rights reserved.	*
  *								*
- * Copyright (c) 2020 YottaDB LLC and/or its subsidiaries.	*
+ * Copyright (c) 2020-2023 YottaDB LLC and/or its subsidiaries.	*
  * All rights reserved.						*
  *								*
  *	This source code contains the intellectual property	*
@@ -333,6 +333,13 @@ bool	mubinccpy (backup_reg_list *list)
 	read_offset = (off_t)BLK_ZERO_OFF(header->start_vbn);
 	for (blk_num_base = 0;  blk_num_base < header->trans_hist.total_blks;  blk_num_base += blks_per_buff)
 	{
+#		ifdef DEBUG
+		if ((0 != ydb_skip_bml_num) && (BLKS_PER_LMAP <= blk_num_base) && (blk_num_base < ydb_skip_bml_num))
+		{
+			read_offset += (bsize * (ydb_skip_bml_num - blk_num_base));
+			blk_num_base = ydb_skip_bml_num;
+		}
+#		endif
 		if (online && (0 != cs_addrs->shmpool_buffer->failed))
 			break;
 		if ((header->trans_hist.total_blks - blk_num_base) < blks_per_buff)
@@ -364,6 +371,10 @@ bool	mubinccpy (backup_reg_list *list)
 		for (i = 0; i < blks_per_buff; i++, bptr = (blk_hdr *)((char *)bptr + bsize))
 		{
 			blk_num = blk_num_base + i;
+#			ifdef DEBUG
+			if ((0 != ydb_skip_bml_num) && (BLKS_PER_LMAP <= blk_num) && (blk_num < ydb_skip_bml_num))
+				continue;
+#			endif
 			if (mu_ctrly_occurred  ||  mu_ctrlc_occurred)
 			{
 				free(outptr);
diff --git a/sr_unix/mupip_restore.c b/sr_unix/mupip_restore.c
index d603e4b41..04b60a92a 100644
--- a/sr_unix/mupip_restore.c
+++ b/sr_unix/mupip_restore.c
@@ -3,7 +3,7 @@
  * Copyright (c) 2001-2020 Fidelity National Information	*
  * Services, Inc. and/or its subsidiaries. All rights reserved.	*
  *								*
- * Copyright (c) 2019-2022 YottaDB LLC and/or its subsidiaries.	*
+ * Copyright (c) 2019-2023 YottaDB LLC and/or its subsidiaries.	*
  * All rights reserved.						*
  *								*
  *	This source code contains the intellectual property	*
@@ -81,6 +81,10 @@ GBLREF	uint4			pipe_child;
 GBLREF	gd_region		*gv_cur_region;
 GBLREF	int4			restore_read_errno;
 
+#ifdef DEBUG
+GBLREF	block_id		ydb_skip_bml_num;
+#endif
+
 LITREF	char			*gtm_dbversion_table[];
 LITREF	char			*mdb_ver_names[];
 
@@ -213,6 +217,11 @@ void mupip_restore(void)
 	}
 	if (udi->fd_opened_with_o_direct)
 		memcpy(&old_data, csd, SGMNT_HDR_LEN);
+#	ifdef DEBUG
+	udi->s_addrs.hdr = &old_data;	/* Now that we have read in the file header, point udi to it for the next dbfilop.
+					 * This is used by the DB_LSEEKREAD macro if "ydb_skip_bml_num" is non-zero.
+					 */
+#	endif
 	if (memcmp(old_data.label, label, GDS_LABEL_SZ) && memcmp(old_data.label, v6_label, GDS_LABEL_SZ))
 	{
 		util_out_print("Output file !AD has an unrecognizable format", TRUE, n_len, db_name);
@@ -421,6 +430,11 @@ void mupip_restore(void)
 				 */
 				new_eof = (off_t)BLK_ZERO_OFF(old_start_vbn) + ((off_t)inhead.db_total_blks * old_blk_size);
 				new_size = new_eof + old_blk_size;
+#				ifdef DEBUG
+				udi->s_addrs.hdr = csd;	/* Point udi to an up to date file header as it is used by the below
+							 * "db_write_eof_block()" call if "ydb_skip_bml_num" is non-zero.
+							 */
+#				endif
 				status = db_write_eof_block(udi, db_fd, old_blk_size, new_eof, &(TREF(dio_buff)));
 				if (0 != status)
 				{
@@ -496,6 +510,10 @@ void mupip_restore(void)
 					bml_newmap((blk_hdr_ptr_t)newmap, BM_SIZE(bplmap), curr_tn, csd->desired_db_format);
 					for (ii = ROUND_UP(old_tot_blks, bplmap); ii < inhead.db_total_blks; ii += bplmap)
 					{
+#						ifdef DEBUG
+						if ((0 != ydb_skip_bml_num) && (0 < ii) && (ii < ydb_skip_bml_num))
+							ii = ydb_skip_bml_num;
+#						endif
 						offset = (off_t)BLK_ZERO_OFF(old_start_vbn) + (off_t)ii * old_blk_size;
 						DB_LSEEKWRITE(NULL, udi, NULL, db_fd, offset, newmap, old_blk_size, status);
 						if (0 != status)
diff --git a/sr_unix/warn_db_sz.c b/sr_unix/warn_db_sz.c
index ecdeecd15..c29087503 100644
--- a/sr_unix/warn_db_sz.c
+++ b/sr_unix/warn_db_sz.c
@@ -3,6 +3,9 @@
  * Copyright (c) 2018-2020 Fidelity National Information	*
  * Services, Inc. and/or its subsidiaries. All rights reserved.	*
  *								*
+ * Copyright (c) 2023 YottaDB LLC and/or its subsidiaries.	*
+ * All rights reserved.						*
+ *								*
  *	This source code contains the intellectual property	*
  *	of its copyright holder(s), and is made available	*
  *	under a license.  If you do not know the terms of	*
@@ -22,12 +25,20 @@
 
 error_def(ERR_LOWSPC);
 
+#ifdef DEBUG
+GBLREF	block_id		ydb_skip_bml_num;
+#endif
+
 void warn_db_sz(char *db_fname, block_id prev_blocks, block_id curr_blocks, block_id tot_blocks)
 {
 	double new_sz_frac;
 	double old_sz_frac;
 	int diff;
 
+#	ifdef DEBUG
+	if (0 != ydb_skip_bml_num)
+		return;	/* Do not issue LOWSPC warning if huge sparse dbs are possible */
+#	endif
 	new_sz_frac = (WBTEST_ENABLED(WBTEST_DB_BLOCKS_WARN)) ?
 			SPCWARNTHRESHOLD : (((double)curr_blocks) / ((double)tot_blocks)) * 100;
 	if (new_sz_frac < SPCWARNTHRESHOLD)