Extended show engine InnoDB status

This feature reorganizes the output of SHOW ENGINE INNODB STATUS to improve readability and to provide additional information. The variable innodb_show_locks_held controls the umber of locks held to print for each InnoDB transaction.

This feature modified the SHOW ENGINE INNODB STATUS command as follows:

• Added extended information about InnoDB internal hash table sizes (in bytes) in the BUFFER POOL AND MEMORY section; also added buffer pool size in bytes.

• Added additional LOG section information.

Other information

• Author / Origin: Baron Schwartz, https://lists.mysql.com/internals/35174

System variables

innodb_show_locks_held

Option	Description
Command-line	Yes
Config file	Yes
Scope	Global
Dynamic	Yes
Data type	ULONG
Default	10
Range	0 - 1000

Specifies the number of locks held to print for each InnoDB transaction in SHOW ENGINE INNODB STATUS.

innodb_print_lock_wait_timeout_info

Option	Description
Command-line	Yes
Config file	Yes
Scope	Global
Dynamic	Yes
Data type	Boolean
Default	OFF

Makes InnoDB to write information about all lock wait timeout errors into the log file.

This allows to find out details about the failed transaction, and, most importantly, the blocking transaction. Query string can be obtained from EVENTS_STATEMENTS_CURRENT table, based on the PROCESSLIST_ID field, which corresponds to thread_id from the log output.

Taking into account that blocking transaction is often a multiple statement one, following query can be used to obtain blocking thread statements history:

SELECT s.SQL_TEXT FROM performance_schema.events_statements_history s
INNER JOIN performance_schema.threads t ON t.THREAD_ID = s.THREAD_ID
WHERE t.PROCESSLIST_ID = %d
UNION
SELECT s.SQL_TEXT FROM performance_schema.events_statements_current s
INNER JOIN performance_schema.threads t ON t.THREAD_ID = s.THREAD_ID
WHERE t.PROCESSLIST_ID = %d;

The PROCESSLIST_ID in this example is exactly the thread id from error log output.

Status variables

The status variables here contain information available in the output of SHOW ENGINE INNODB STATUS, organized by the sections SHOW ENGINE INNODB STATUS displays. If you are familiar with the output of SHOW ENGINE INNODB STATUS, you will probably already recognize the information these variables contain.

BACKGROUND THREAD

The following variables contain information in the BACKGROUND THREAD section of the output from SHOW ENGINE INNODB STATUS.

Expected output

-----------------
BACKGROUND THREAD
-----------------
srv_master_thread loops: 1 srv_active, 0 srv_shutdown, 11844 srv_idle
srv_master_thread log flush and writes: 11844

InnoDB has a source thread which performs background tasks depending on the server state, once per second. If the server is under workload, the source thread runs the following: performs background table drops; performs change buffer merge, adaptively; flushes the redo log to disk; evicts tables from the dictionary cache if needed to satisfy its size limit; makes a checkpoint. If the server is idle: performs background table drops, flushes and/or checkpoints the redo log if needed due to the checkpoint age; performs change buffer merge at full I/O capacity; evicts tables from the dictionary cache if needed; and makes a checkpoint.

Innodb_master_thread_active_loops

Option	Description
Scope	Global
Data type	Numeric

This variable shows the number of times the above one-second loop was executed for active server states.

Innodb_master_thread_idle_loops

Option	Description
Scope	Global
Data type	Numeric

This variable shows the number of times the above one-second loop was executed for idle server states.

Innodb_background_log_sync

Option	Description
Scope	Global
Data type	Numeric

This variable shows the number of times the InnoDB source thread has written and flushed the redo log.

SEMAPHORES

The following variables contain information in the SEMAPHORES section of the output from SHOW ENGINE INNODB STATUS. An example of that output is:

Expected output

----------
SEMAPHORES
----------
OS WAIT ARRAY INFO: reservation count 9664, signal count 11182
Mutex spin waits 20599, rounds 223821, OS waits 4479
RW-shared spins 5155, OS waits 1678; RW-excl spins 5632, OS waits 2592
Spin rounds per wait: 10.87 mutex, 15.01 RW-shared, 27.19 RW-excl

INSERT BUFFER AND ADAPTIVE HASH INDEX

The following variables contain information in the INSERT BUFFER AND ADAPTIVE HASH INDEX section of the output from SHOW ENGINE INNODB STATUS. An example of that output is:

Expected output

-------------------------------------
INSERT BUFFER AND ADAPTIVE HASH INDEX
-------------------------------------
Ibuf: size 1, free list len 6089, seg size 6091,
44497 inserts, 44497 merged recs, 8734 merges
0.00 hash searches/s, 0.00 non-hash searches/s

Innodb_ibuf_free_list

Option	Description
Scope	Global
Data type	Numeric

Innodb_ibuf_segment_size

Option	Description
Scope	Global
Data type	Numeric

LOG

The following variables contain information in the LOG section of the output from SHOW ENGINE INNODB STATUS. An example of that output is:

Expected output

LOG
---
Log sequence number 10145937666
Log flushed up to   10145937666
Pages flushed up to 10145937666
Last checkpoint at  10145937666
Max checkpoint age    80826164
Checkpoint age target 78300347
Modified age          0
Checkpoint age        0
0 pending log writes, 0 pending chkp writes
9 log i/o's done, 0.00 log i/o's/second
Log tracking enabled
Log tracked up to   10145937666
Max tracked LSN age 80826164

Innodb_lsn_current

Option	Description
Scope	Global
Data type	Numeric

This variable shows the current log sequence number.

Innodb_lsn_flushed

Option	Description
Scope	Global
Data type	Numeric

This variable shows the current maximum LSN that has been written and flushed to disk.

Innodb_lsn_last_checkpoint

Option	Description
Scope	Global
Data type	Numeric

This variable shows the LSN of the latest completed checkpoint.

Innodb_checkpoint_age

Option	Description
Scope	Global
Data type	Numeric

This variable shows the current InnoDB checkpoint age, i.e., the difference between the current LSN and the LSN of the last completed checkpoint.

Innodb_checkpoint_max_age

Option	Description
Scope	Global
Data type	Numeric

This variable shows the maximum allowed checkpoint age above which the redo log is close to full and a checkpoint must happen before any further redo log writes.

Note

This variable was removed in Percona Server for MySQL 8.0.13-4 due to a change in MySQL. The variable is identical to log capacity.

BUFFER POOL AND MEMORY

The following variables contain information in the BUFFER POOL AND MEMORY section of the output from SHOW ENGINE INNODB STATUS. An example of that output is:

Expected output

----------------------
BUFFER POOL AND MEMORY
----------------------
Total memory allocated 137363456; in additional pool allocated 0
Total memory allocated by read views 88
Internal hash tables (constant factor + variable factor)
    Adaptive hash index 2266736         (2213368 + 53368)
    Page hash           139112 (buffer pool 0 only)
    Dictionary cache    729463  (554768 + 174695)
    File system         824800  (812272 + 12528)
    Lock system         333248  (332872 + 376)
    Recovery system     0       (0 + 0)
Dictionary memory allocated 174695
Buffer pool size        8191
Buffer pool size, bytes 134201344
Free buffers            7481
Database pages          707
Old database pages      280
Modified db pages       0
Pending reads 0
Pending writes: LRU 0, flush list 0 single page 0
Pages made young 0, not young 0
0.00 youngs/s, 0.00 non-youngs/s
Pages read 707, created 0, written 1
0.00 reads/s, 0.00 creates/s, 0.00 writes/s
No buffer pool page gets since the last printout
Pages read ahead 0.00/s, evicted without access 0.00/s, Random read ahead 0.00/s
LRU len: 707, unzip_LRU len: 0

Innodb_mem_adaptive_hash

Option	Description
Scope	Global
Data type	Numeric

This variable shows the current size, in bytes, of the adaptive hash index.

Innodb_mem_dictionary

Option	Description
Scope	Global
Data type	Numeric

This variable shows the current size, in bytes, of the InnoDB in-memory data dictionary info.

Innodb_mem_total

Option	Description
Scope	Global
Data type	Numeric

This variable shows the total amount of memory, in bytes, InnoDB has allocated in the process heap memory.

Innodb_buffer_pool_pages_LRU_flushed

Option	Description
Scope	Global
Data type	Numeric

This variable shows the total number of buffer pool pages which have been flushed from the LRU list, i.e., too old pages which had to be flushed in order to make buffer pool room to read in new data pages.

Innodb_buffer_pool_pages_made_not_young

Option	Description
Scope	Global
Data type	Numeric

This variable shows the number of times a buffer pool page was not marked as accessed recently in the LRU list because of innodb_old_blocks_time variable setting.

Innodb_buffer_pool_pages_made_young

Option	Description
Scope	Global
Data type	Numeric

This variable shows the number of times a buffer pool page was moved to the young end of the LRU list due to its access, to prevent its eviction from the buffer pool.

Innodb_buffer_pool_pages_old

Option	Description
Scope	Global
Data type	Numeric

This variable shows the total number of buffer pool pages which are considered to be old according to the Making the Buffer Pool Scan Resistant manual page.

TRANSACTIONS

The following variables contain information in the TRANSACTIONS section of the output from SHOW INNODB STATUS. An example of that output is:

Expected output

------------
TRANSACTIONS
------------
Trx id counter F561FD
Purge done for trx's n:o < F561EB undo n:o < 0
History list length 19
LIST OF TRANSACTIONS FOR EACH SESSION:
---TRANSACTION 0, not started, process no 993, OS thread id 140213152634640
mysql thread id 15933, query id 32109 localhost root
show innodb status
---TRANSACTION F561FC, ACTIVE 29 sec, process no 993, OS thread id 140213152769808 updating or deleting
mysql tables in use 1, locked 1

Innodb_max_trx_id

Option	Description
Scope	Global
Data type	Numeric

This variable shows the next free transaction id number.

Innodb_oldest_view_low_limit_trx_id

Option	Description
Scope	Global
Data type	Numeric

This variable shows the highest transaction id, above which the current oldest open read view does not see any transaction changes. Zero if there is no open view.

Innodb_purge_trx_id

Option	Description
Scope	Global
Data type	Numeric

This variable shows the oldest transaction id whose records have not been purged yet.

Innodb_purge_undo_no

Option	Description
Scope	Global
Data type	Numeric

INFORMATION_SCHEMA Tables

The following table contains information about the oldest active transaction in the system.

INFORMATION_SCHEMA.XTRADB_READ_VIEW

Column Name	Description
‘READ_VIEW_LOW_LIMIT_TRX_NUMBER’	This is the highest transactions number at the time the view was created.
‘READ_VIEW_UPPER_LIMIT_TRX_ID’	This is the highest transactions ID at the time the view was created. This means that it should not see newer transactions with IDs bigger than or equal to that value.
‘READ_VIEW_LOW_LIMIT_TRX_ID’	This is the latest committed transaction ID at the time the oldest view was created. This means that it should see all transactions with IDs smaller than or equal to that value.

Note

Starting with Percona Server for MySQL 8.0.20-11, in INFORMATION_SCHEMA.XTRADB_READ_VIEW, the data type for the following columns is changed from VARCHAR(18) to BIGINT UNSIGNED:

• READ_VIEW_LOW_LIMIT_TRX_NUMBER

• READ_VIEW_UPPER_LIMIT_TRX_ID

• READ_VIWE_LOW_LIMIT_TRX_ID

The columns contain 64-bit integers, which is too large for VARCHAR(18).

The following table contains information about the memory usage for InnoDB/XtraDB hash tables.

INFORMATION_SCHEMA.XTRADB_INTERNAL_HASH_TABLES

Column Name	Description
‘INTERNAL_HASH_TABLE_NAME’	Hash table name
‘TOTAL_MEMORY’	Total amount of memory
‘CONSTANT_MEMORY’	Constant memory
‘VARIABLE_MEMORY’	Variable memory

Other reading

• SHOW INNODB STATUS walk through

• Table locks in SHOW INNODB STATUS

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Last update: 2023-01-12