MySQL information schema learning (II) -- InnoDB table

Learn about and innodb Related table .

1.INNODB_TRX

        Provide information about each transaction currently executed internally Information about InnoDB, Including whether the transaction is waiting for locking 、 When the transaction starts and what the transaction is executing SQL sentence . 

The main Column ：

• TRX_ID  The only business ID Number

• TRX_WEIGHT  The weight of the transaction , reflect （ But not necessarily the exact count ） Number of rows changed and transaction locked . In order to solve the deadlock , InnoDB Select the transaction with the smallest weight as “ The victim ” Roll back . Transactions that have changed non transactional tables are considered heavier than other transactions , No matter how many rows are changed and locked .

• TRX_STATE  Transaction execution status . The allowed values are  RUNNING、LOCK WAIT、 ROLLING BACK and  COMMITTING. You can judge whether a certain current transaction is waiting for a lock

• TRX_STARTED  Transaction start time .

• TRX_REQUESTED_LOCK_ID  The lock that the transaction is currently waiting for ID, If TRX_STATE yes LOCK WAIT; otherwise NULL. To get more information about locks , Please compare this column with the  LOCK_ID Column Connect INNODB_LOCKS.

You can get the lock that the current transaction is waiting for , Easy to analyze deadlock problems .

• TRX_WAIT_STARTED  The time when the transaction starts waiting for the lock , If  TRX_STATE yes LOCK WAIT; otherwise NULL.

• TRX_MYSQL_THREAD_ID MySQL Threads ID. To get more information about threads , Please compare this column with the ID Column Connect INFORMATION_SCHEMA PROCESSLIST

• TRX_QUERY  The transaction is executing SQL sentence .

• TRX_OPERATION_STATE  The current operation of the transaction , If any ; otherwise  NULL.

• TRX_TABLES_IN_USE InnoDB Process the current SQL Use   The number of watches .

• TRX_TABLES_LOCKED InnoDB At present SQL Statement has a row lock   Number of tables for .（ Because these are row locks , Not a watch lock , So although some rows are locked , However, tables can usually still be read and written by multiple transactions .）

• TRX_LOCK_STRUCTS  Number of locks reserved by transaction .

• TRX_LOCK_MEMORY_BYTES  The total size of the lock structure of this transaction in memory .

• TRX_ROWS_LOCKED  The approximate number or rows locked by this transaction . The value may include delete tag lines that actually exist but are not visible to the transaction .

• TRX_ROWS_MODIFIED  Number of rows modified and inserted in this transaction .

• TRX_CONCURRENCY_TICKETS  A value , Indicates how much work the current transaction can do before it is swapped out , from  innodb_concurrency_tickets  The system variable specifies .

• TRX_ISOLATION_LEVEL  Isolation level of the current transaction .

• TRX_UNIQUE_CHECKS  Whether to turn unique checking on or off for the current transaction . for example , They may be turned off during bulk data loading .

• TRX_FOREIGN_KEY_CHECKS  Whether to turn foreign key checking on or off for the current transaction . for example , They may be turned off during bulk data loading .

• TRX_LAST_FOREIGN_KEY_ERROR  Detailed error information of the last foreign key error , If any ; otherwise NULL.

• TRX_ADAPTIVE_HASH_LATCHED  Whether the adaptive hash index is locked by the current transaction . When the adaptive hash index search system is partitioned , A single transaction does not lock the entire adaptive hash index . The adaptive hash index partition is created by control  innodb_adaptive_hash_index_parts, The default setting is 8.

• TRX_ADAPTIVE_HASH_TIMEOUT  Whether to discard the search latch of adaptive hash index immediately , Or from MySQL Keep it in the call of . When there is no adaptive hash index contention , This value remains at zero , And statements retain latches until they are complete . During the dispute , It counts down to zero , And the statement releases the latch immediately after each line lookup . When the adaptive hash index search system is partitioned （ from control  innodb_adaptive_hash_index_parts） when , This value remains at 0.

• TRX_IS_READ_ONLY  value 1 Indicates that the transaction is read-only .

• TRX_AUTOCOMMIT_NON_LOCKING  value 1 Indicates that the transaction is  SELECT Don't use FOR UPDATEorLOCK IN SHARED MODE Statement of clause , And execute when enabled , autocommit Therefore, the transaction only contains this statement . When this column and TRX_IS_READ_ONLY Are all 1 when , InnoDB Optimize transactions to reduce the overhead associated with transactions that change table data .

2.INNODB_LOCKS

Provide relevant InnoDB  Information about each lock that the transaction has requested but has not yet acquired , And the information held by the transaction blocking each lock of another transaction . Main column ：

• LOCK_ID  A unique lock ID Number

• LOCK_TRX_ID  Of the transaction that holds the lock ID. To get detailed information about transactions , Please compare this column with the  TRX_ID Column Connect INNODB_TRX.

• LOCK_MODE  How to request a lock . The allowed lock mode descriptors are  S, X, IS, IX, GAP, AUTO_INC, and  UNKNOWN. Lock mode descriptors can be used in combination to identify specific lock modes .

• LOCK_TYPE  The type of lock . Allowed value  RECORD Applicable to row level lock 、 TABLE Table lock .

• LOCK_TABLE  The name of the table that has or contains the locked record .

• LOCK_INDEX  Name of index , If LOCK_TYPE yes  RECORD;  otherwise NULL.

• LOCK_SPACE  Lock the table space of the record ID, If  LOCK_TYPE yes RECORD;  otherwise NULL.

• LOCK_PAGE  Lock the page number of the record , If  LOCK_TYPE yes RECORD;  otherwise NULL.

• LOCK_REC  The heap number of the locked record in the page , If  LOCK_TYPE yes RECORD;  otherwise NULL.

3.INNODB_LOCK_WAIT

Contains each block InnoDB  One or more rows of a transaction , Indicates the lock it has requested and any locks that block the request .

Main column ：

• REQUESTING_TRX_ID  request （ Blocking ） The transaction ID.

• REQUESTED_LOCK_ID  The lock that the transaction is waiting for ID. To get more information about locks , Please compare this column with the  LOCK_ID Column Connect INNODB_LOCKS.

• BLOCKING_TRX_ID  Blocking a transaction ID.

• BLOCKING_LOCK_ID  A transaction holds a lock ID, This transaction prevents another transaction from continuing . To get more information about locks , Please compare this column with the LOCK_ID Column connection INNODB_LOCKS.

trx Table describes transactions ,lock Table describes the lock ,lock_wait Describes the relationship between blocking transaction locks .

for instance , Create a new table members

Start transaction 1 

start TRANSACTION;
SELECT * FROM members WHERE id = 1 for UPDATE;

Start transaction 2

start TRANSACTION;
SELECT * FROM members WHERE id = 1 for UPDATE;

Observe the present 3 The state of the table ：

Business table   There are currently two transactions 1 and 2 Business 1 Running   Business 2 Waiting for lock

Lock table   There is currently a lock , Business 1,2 Are requesting row locks

  Lock wait list   Business 1 Waiting for transaction 2 Lock of

Later, learn to use these tables to diagnose and analyze problems .