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MDEV-38315 Optimize NULL only reads for wide tables in core engines #4627

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782c896
MDEV-38315 Optimize NULL only reads for wide tables in core engines
alexaustin007 Feb 6, 2026
2e3b05a
MDEV-38315 Optimize NULL only reads for InnoDB, Aria and MyISAM
alexaustin007 Feb 7, 2026
8954531
MDEV-38315 Add NULL-only read optimization for core engines
alexaustin007 Feb 13, 2026
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7 changes: 7 additions & 0 deletions include/myisam.h
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Original file line number Diff line number Diff line change
Expand Up @@ -224,13 +224,20 @@ struct st_mi_bit_buff;
type, length, null_bit and null_pos
*/

#define MI_NO_FIELD_NR 0xFFFFU

typedef struct st_columndef /* column information */
{
enum en_fieldtype type;
uint16 length; /* length of field */
uint32 offset; /* Offset to position in row */
uint8 null_bit; /* If column may be 0 */
uint16 null_pos; /* position for null marker */
/*
SQL column number for this recinfo entry, when known.
Entries that only represent packed/null marker bytes are MI_NO_FIELD_NR.
*/
uint16 fieldnr;

#ifndef NOT_PACKED_DATABASES
void (*unpack)(struct st_columndef *rec,struct st_mi_bit_buff *buff,
Expand Down
167 changes: 167 additions & 0 deletions mysql-test/suite/innodb/r/innodb_null_only.result
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@@ -0,0 +1,167 @@
SET GLOBAL innodb_monitor_disable='module_buffer_page';
SET GLOBAL innodb_monitor_reset_all='module_buffer_page';
SET GLOBAL innodb_monitor_enable='module_buffer_page';
CREATE TABLE t (
id INT PRIMARY KEY,
b MEDIUMBLOB NULL,
c INT NOT NULL
) ENGINE=InnoDB;
INSERT INTO t VALUES
(1, REPEAT('a', 100000), 1),
(2, NULL, 2),
(3, REPEAT('b', 100000), 3),
(4, NULL, 4);
# Restart to flush buffer pool state before measuring blob page reads.
SET GLOBAL innodb_monitor_disable='module_buffer_page';
SET GLOBAL innodb_monitor_reset_all='module_buffer_page';
SET GLOBAL innodb_monitor_enable='module_buffer_page';
FLUSH STATUS;
SELECT COUNT(*) FROM t WHERE b IS NULL;
COUNT(*)
2
SELECT VARIABLE_VALUE > 0 AS null_only_used
FROM information_schema.session_status
WHERE VARIABLE_NAME='Handler_null_only_columns';
null_only_used
1
SELECT SUM(COUNT) AS blob_reads
FROM information_schema.innodb_metrics
WHERE NAME IN ('buffer_page_read_blob','buffer_page_read_zblob',
'buffer_page_read_zblob2');
blob_reads
0
SET GLOBAL innodb_monitor_disable='module_buffer_page';
SET GLOBAL innodb_monitor_reset_all='module_buffer_page';
SET GLOBAL innodb_monitor_enable='module_buffer_page';
FLUSH STATUS;
SELECT COUNT(*) FROM t WHERE b <=> NULL;
COUNT(*)
2
SELECT VARIABLE_VALUE > 0 AS null_only_used
FROM information_schema.session_status
WHERE VARIABLE_NAME='Handler_null_only_columns';
null_only_used
1
SELECT SUM(COUNT) AS blob_reads
FROM information_schema.innodb_metrics
WHERE NAME IN ('buffer_page_read_blob','buffer_page_read_zblob',
'buffer_page_read_zblob2');
blob_reads
0
FLUSH STATUS;
SELECT COUNT(*)
FROM t t1 JOIN t t2
ON t1.id= t2.id AND t1.b IS NULL;
COUNT(*)
2
SELECT VARIABLE_VALUE > 0 AS null_only_used
FROM information_schema.session_status
WHERE VARIABLE_NAME='Handler_null_only_columns';
null_only_used
1
FLUSH STATUS;
SELECT COUNT(*)
FROM t outer_t
WHERE EXISTS (SELECT 1
FROM t inner_t
WHERE inner_t.id= outer_t.id
AND inner_t.b IS NULL);
COUNT(*)
2
SELECT VARIABLE_VALUE > 0 AS null_only_used
FROM information_schema.session_status
WHERE VARIABLE_NAME='Handler_null_only_columns';
null_only_used
1
SET GLOBAL innodb_monitor_disable='module_buffer_page';
SET GLOBAL innodb_monitor_reset_all='module_buffer_page';
SET GLOBAL innodb_monitor_enable='module_buffer_page';
FLUSH STATUS;
SELECT SUM(CRC32(b)) FROM t WHERE b IS NULL OR c = 3;
SUM(CRC32(b))
4149198040
SELECT VARIABLE_VALUE = 0 AS null_only_used
FROM information_schema.session_status
WHERE VARIABLE_NAME='Handler_null_only_columns';
null_only_used
1
SELECT SUM(COUNT) > 0 AS blob_reads
FROM information_schema.innodb_metrics
WHERE NAME IN ('buffer_page_read_blob','buffer_page_read_zblob',
'buffer_page_read_zblob2');
blob_reads
1
# Restart to force disk reads for the FOR UPDATE guardrail check.
SET GLOBAL innodb_monitor_disable='module_buffer_page';
SET GLOBAL innodb_monitor_reset_all='module_buffer_page';
SET GLOBAL innodb_monitor_enable='module_buffer_page';
SELECT c FROM t WHERE b IS NULL FOR UPDATE;
c
2
4
COMMIT;
SELECT SUM(COUNT) > 0 AS blob_reads
FROM information_schema.innodb_metrics
WHERE NAME IN ('buffer_page_read_blob','buffer_page_read_zblob',
'buffer_page_read_zblob2');
blob_reads
1
DROP TABLE t;
# ICP check: c-range on leading key part and direct NULL predicate
# on second key part (d) should use index condition pushdown.
CREATE TABLE t_icp (
id INT PRIMARY KEY,
c INT NOT NULL,
d VARCHAR(64) NULL,
payload INT NOT NULL,
KEY idx_cd (c, d)
) ENGINE=InnoDB;
INSERT INTO t_icp VALUES
(1, 1, 'x', 10),
(2, 2, NULL, 20),
(3, 3, 'y', 30),
(4, 4, NULL, 40);
SET optimizer_switch='index_condition_pushdown=on';
FLUSH STATUS;
EXPLAIN SELECT payload
FROM t_icp FORCE INDEX (idx_cd)
WHERE c > 0 AND d IS NULL;
id select_type table type possible_keys key key_len ref rows Extra
# SIMPLE t_icp range idx_cd idx_cd # # # Using index condition
SELECT SUM(payload)
FROM t_icp FORCE INDEX (idx_cd)
WHERE c > 0 AND d IS NULL;
SUM(payload)
60
SELECT VARIABLE_VALUE > 0 AS icp_used
FROM information_schema.session_status
WHERE VARIABLE_NAME='HANDLER_ICP_ATTEMPTS';
icp_used
1
DROP TABLE t_icp;
CREATE TABLE t_vcol (
id INT PRIMARY KEY,
b MEDIUMBLOB NULL,
v VARBINARY(1) AS (SUBSTR(b, 1, 1)) VIRTUAL
) ENGINE=InnoDB;
INSERT INTO t_vcol (id, b) VALUES
(1, REPEAT('a', 100000)),
(2, NULL),
(3, REPEAT('b', 100000)),
(4, NULL);
# Restart to validate virtual-column guardrail with cold-page metrics.
SET GLOBAL innodb_monitor_disable='module_buffer_page';
SET GLOBAL innodb_monitor_reset_all='module_buffer_page';
SET GLOBAL innodb_monitor_enable='module_buffer_page';
SELECT COUNT(*) FROM t_vcol WHERE v IS NULL;
COUNT(*)
2
SELECT SUM(COUNT) > 0 AS blob_reads
FROM information_schema.innodb_metrics
WHERE NAME IN ('buffer_page_read_blob','buffer_page_read_zblob',
'buffer_page_read_zblob2');
blob_reads
1
DROP TABLE t_vcol;
SET GLOBAL innodb_monitor_disable='module_buffer_page';
SET GLOBAL innodb_monitor_reset_all='module_buffer_page';
187 changes: 187 additions & 0 deletions mysql-test/suite/innodb/t/innodb_null_only.test
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@@ -0,0 +1,187 @@
--source innodb_default_row_format.inc

--disable_warnings
SET GLOBAL innodb_monitor_disable='module_buffer_page';
SET GLOBAL innodb_monitor_reset_all='module_buffer_page';
SET GLOBAL innodb_monitor_enable='module_buffer_page';
--enable_warnings

CREATE TABLE t (
id INT PRIMARY KEY,
b MEDIUMBLOB NULL,
c INT NOT NULL
) ENGINE=InnoDB;

INSERT INTO t VALUES
(1, REPEAT('a', 100000), 1),
(2, NULL, 2),
(3, REPEAT('b', 100000), 3),
(4, NULL, 4);

--let $restart_noprint=2
--echo # Restart to flush buffer pool state before measuring blob page reads.
--let $restart_parameters=--innodb-buffer-pool-load-at-startup=0 --innodb-buffer-pool-dump-at-shutdown=0
--source include/restart_mysqld.inc
--let $restart_parameters=

--disable_warnings
SET GLOBAL innodb_monitor_disable='module_buffer_page';
SET GLOBAL innodb_monitor_reset_all='module_buffer_page';
SET GLOBAL innodb_monitor_enable='module_buffer_page';
--enable_warnings

FLUSH STATUS;
SELECT COUNT(*) FROM t WHERE b IS NULL;
SELECT VARIABLE_VALUE > 0 AS null_only_used
FROM information_schema.session_status
WHERE VARIABLE_NAME='Handler_null_only_columns';

SELECT SUM(COUNT) AS blob_reads
FROM information_schema.innodb_metrics
WHERE NAME IN ('buffer_page_read_blob','buffer_page_read_zblob',
'buffer_page_read_zblob2');

--disable_warnings
SET GLOBAL innodb_monitor_disable='module_buffer_page';
SET GLOBAL innodb_monitor_reset_all='module_buffer_page';
SET GLOBAL innodb_monitor_enable='module_buffer_page';
--enable_warnings

FLUSH STATUS;
SELECT COUNT(*) FROM t WHERE b <=> NULL;
SELECT VARIABLE_VALUE > 0 AS null_only_used
FROM information_schema.session_status
WHERE VARIABLE_NAME='Handler_null_only_columns';

SELECT SUM(COUNT) AS blob_reads
FROM information_schema.innodb_metrics
WHERE NAME IN ('buffer_page_read_blob','buffer_page_read_zblob',
'buffer_page_read_zblob2');

FLUSH STATUS;
SELECT COUNT(*)
FROM t t1 JOIN t t2
ON t1.id= t2.id AND t1.b IS NULL;
SELECT VARIABLE_VALUE > 0 AS null_only_used
FROM information_schema.session_status
WHERE VARIABLE_NAME='Handler_null_only_columns';

FLUSH STATUS;
SELECT COUNT(*)
FROM t outer_t
WHERE EXISTS (SELECT 1
FROM t inner_t
WHERE inner_t.id= outer_t.id
AND inner_t.b IS NULL);
SELECT VARIABLE_VALUE > 0 AS null_only_used
FROM information_schema.session_status
WHERE VARIABLE_NAME='Handler_null_only_columns';

--disable_warnings
SET GLOBAL innodb_monitor_disable='module_buffer_page';
SET GLOBAL innodb_monitor_reset_all='module_buffer_page';
SET GLOBAL innodb_monitor_enable='module_buffer_page';
--enable_warnings

FLUSH STATUS;
SELECT SUM(CRC32(b)) FROM t WHERE b IS NULL OR c = 3;
SELECT VARIABLE_VALUE = 0 AS null_only_used
FROM information_schema.session_status
WHERE VARIABLE_NAME='Handler_null_only_columns';

SELECT SUM(COUNT) > 0 AS blob_reads
FROM information_schema.innodb_metrics
WHERE NAME IN ('buffer_page_read_blob','buffer_page_read_zblob',
'buffer_page_read_zblob2');

--let $restart_parameters=--innodb-buffer-pool-load-at-startup=0 --innodb-buffer-pool-dump-at-shutdown=0
--echo # Restart to force disk reads for the FOR UPDATE guardrail check.
--source include/restart_mysqld.inc
--let $restart_parameters=

--disable_warnings
SET GLOBAL innodb_monitor_disable='module_buffer_page';
SET GLOBAL innodb_monitor_reset_all='module_buffer_page';
SET GLOBAL innodb_monitor_enable='module_buffer_page';
--enable_warnings

SELECT c FROM t WHERE b IS NULL FOR UPDATE;
COMMIT;

SELECT SUM(COUNT) > 0 AS blob_reads
FROM information_schema.innodb_metrics
WHERE NAME IN ('buffer_page_read_blob','buffer_page_read_zblob',
'buffer_page_read_zblob2');

DROP TABLE t;

--echo # ICP check: c-range on leading key part and direct NULL predicate
--echo # on second key part (d) should use index condition pushdown.
CREATE TABLE t_icp (
id INT PRIMARY KEY,
c INT NOT NULL,
d VARCHAR(64) NULL,
payload INT NOT NULL,
KEY idx_cd (c, d)
) ENGINE=InnoDB;

INSERT INTO t_icp VALUES
(1, 1, 'x', 10),
(2, 2, NULL, 20),
(3, 3, 'y', 30),
(4, 4, NULL, 40);

SET optimizer_switch='index_condition_pushdown=on';
FLUSH STATUS;

--replace_column 1 # 7 # 8 # 9 #
EXPLAIN SELECT payload
FROM t_icp FORCE INDEX (idx_cd)
WHERE c > 0 AND d IS NULL;

SELECT SUM(payload)
FROM t_icp FORCE INDEX (idx_cd)
WHERE c > 0 AND d IS NULL;

SELECT VARIABLE_VALUE > 0 AS icp_used
FROM information_schema.session_status
WHERE VARIABLE_NAME='HANDLER_ICP_ATTEMPTS';

DROP TABLE t_icp;

CREATE TABLE t_vcol (
id INT PRIMARY KEY,
b MEDIUMBLOB NULL,
v VARBINARY(1) AS (SUBSTR(b, 1, 1)) VIRTUAL
) ENGINE=InnoDB;

INSERT INTO t_vcol (id, b) VALUES
(1, REPEAT('a', 100000)),
(2, NULL),
(3, REPEAT('b', 100000)),
(4, NULL);

--let $restart_parameters=--innodb-buffer-pool-load-at-startup=0 --innodb-buffer-pool-dump-at-shutdown=0
--echo # Restart to validate virtual-column guardrail with cold-page metrics.
--source include/restart_mysqld.inc
--let $restart_parameters=

--disable_warnings
SET GLOBAL innodb_monitor_disable='module_buffer_page';
SET GLOBAL innodb_monitor_reset_all='module_buffer_page';
SET GLOBAL innodb_monitor_enable='module_buffer_page';
--enable_warnings

SELECT COUNT(*) FROM t_vcol WHERE v IS NULL;

SELECT SUM(COUNT) > 0 AS blob_reads
FROM information_schema.innodb_metrics
WHERE NAME IN ('buffer_page_read_blob','buffer_page_read_zblob',
'buffer_page_read_zblob2');

DROP TABLE t_vcol;

--disable_warnings
SET GLOBAL innodb_monitor_disable='module_buffer_page';
SET GLOBAL innodb_monitor_reset_all='module_buffer_page';
--enable_warnings
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