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

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

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316cd29
MDEV-38315 Optimize NULL only reads for wide tables in core engines
alexaustin007 Feb 6, 2026
04e5ea8
MDEV-38315 Optimize NULL only reads for InnoDB, Aria and MyISAM
alexaustin007 Feb 7, 2026
68d80b3
MDEV-38315 Add NULL-only read optimization for core engines
alexaustin007 Feb 13, 2026
99ef1bb
MDEV-38315 Remove handler flag, fixed whitespace issue
alexaustin007 Feb 20, 2026
5b10588
MDEV-38315 Re-record tests affected by new status variable
alexaustin007 Feb 20, 2026
488e818
MDEV-38315 Narrow null-only optimization to InnoDB
alexaustin007 Mar 1, 2026
5bd2538
MDEV-38315 Fix null-only status accounting
alexaustin007 Apr 14, 2026
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1 change: 0 additions & 1 deletion include/myisam.h
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Original file line number Diff line number Diff line change
Expand Up @@ -231,7 +231,6 @@ typedef struct st_columndef /* column information */
uint32 offset; /* Offset to position in row */
uint8 null_bit; /* If column may be 0 */
uint16 null_pos; /* position for null marker */

#ifndef NOT_PACKED_DATABASES
void (*unpack)(struct st_columndef *rec,struct st_mi_bit_buff *buff,
uchar *start,uchar *end);
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211 changes: 211 additions & 0 deletions mysql-test/suite/innodb/r/innodb_null_only.result
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Original file line number Diff line number Diff line change
@@ -0,0 +1,211 @@
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 with buffer pool dump/load disabled so blob-page-read metrics
# reflect a cold cache, not pages left from table setup.
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';
# Reset innodb_metrics only before blob-read checks; use FLUSH STATUS
# to isolate per-query session status like Null_only_columns.
FLUSH STATUS;
SELECT COUNT(*) FROM t WHERE b IS NULL;
COUNT(*)
2
SELECT VARIABLE_VALUE AS null_only_columns
FROM information_schema.session_status
WHERE VARIABLE_NAME='Null_only_columns';
null_only_columns
1
# Sum the three blob-page-read counters to cover uncompressed and
# compressed off-page blob representations in one assertion.
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 WHERE b <=> NULL;
COUNT(*)
2
SELECT VARIABLE_VALUE AS null_only_columns
FROM information_schema.session_status
WHERE VARIABLE_NAME='Null_only_columns';
null_only_columns
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;
# Positive case: ON-clause shape should still mark the
# column as null-only and avoid off-page blob reads.
SELECT COUNT(*)
FROM t t1 JOIN t t2
ON t1.id= t2.id AND t1.b IS NULL;
COUNT(*)
2
SELECT VARIABLE_VALUE AS null_only_columns
FROM information_schema.session_status
WHERE VARIABLE_NAME='Null_only_columns';
null_only_columns
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;
# Positive case: EXISTS shape should still mark the
# column as null-only and avoid off-page blob reads.
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 AS null_only_columns
FROM information_schema.session_status
WHERE VARIABLE_NAME='Null_only_columns';
null_only_columns
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;
# Negative case: CRC32(b) needs the actual blob value, so SQL should
# clear the null-only candidate and InnoDB should read blob pages.
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='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';
FLUSH STATUS;
# FOR UPDATE keeps the SQL-layer candidate, but InnoDB disables the
# optimization under LOCK_X and should still read blob pages.
SELECT c FROM t WHERE b IS NULL FOR UPDATE;
c
2
4
SELECT VARIABLE_VALUE AS null_only_columns
FROM information_schema.session_status
WHERE VARIABLE_NAME='Null_only_columns';
null_only_columns
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
DROP TABLE t;
# ICP check: the same query should explain and execute with index
# condition pushdown, while SQL still marks d IS NULL as null-only.
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 payload
FROM t_icp FORCE INDEX (idx_cd)
WHERE c > 0 AND d IS NULL;
payload
20
40
SELECT VARIABLE_VALUE AS null_only_columns
FROM information_schema.session_status
WHERE VARIABLE_NAME='Null_only_columns';
null_only_columns
1
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';
FLUSH STATUS;
# Virtual-column guardrail: SQL should not mark v as null-only, so
# the query should still force blob-page reads.
SELECT COUNT(*) FROM t_vcol WHERE v IS NULL;
COUNT(*)
2
SELECT VARIABLE_VALUE AS null_only_columns
FROM information_schema.session_status
WHERE VARIABLE_NAME='Null_only_columns';
null_only_columns
0
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';
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