Why to avoid big business and how to solve big business?


What is a big deal

The running time is relatively long, and the transaction that has not been committed for a long time can be called a large transaction

The cause of big business

  • The operation data is quite large
  • A lot of lock competition
  • There are other non DB time-consuming operations in the transaction
  • 。。。

The impact of big business

  • In the case of concurrency, the database connection pool is easy to burst
  • Lock too much data, causing a lot of blocking and lock timeout
  • Long execution time, easy to cause master-slave delay
  • Rollback takes a long time
  • Undo log inflation
  • 。。。

How to query big business

notesThe operation of SQL in this paper is based on MySQL 5.7

Take the transaction whose query execution time exceeds 10 seconds as an example

select * from information_schema.innodb_trx where TIME_TO_SEC(timediff(now(),trx_started))>10

How to avoid big business

General solution

  • In a transaction, avoid processing too much data at one time
  • In a transaction, try to avoid unnecessary queries
  • In a transaction, avoid time-consuming operations, resulting in transaction timeout. Some non DB operations, such as RPC calls and message queuing operations, should be put out of the transaction as far as possible

Solution based on mysql5.7

  • In InnoDB transactions, row locks are added when they are needed, but they are not released immediately when they are not needed. Instead, they are not released until the end of the transaction.If you need to lock multiple rows in a transaction, put back the locks that are most likely to cause lock conflicts and affect concurrency
  • Through setmax_ EXECUTION_ Time command to control the maximum query time of each statement to avoid the accidental query time of a single statement
  • Monitoring information_ schema.Innodb_ TRX table, set long transaction threshold, alarm and / or kill if exceeding
  • In the business function test phase, it is required to output all general_ Log, analyze log behavior and find problems in advance
  • Setting InnoDB_ undo_ The table spaces value separates undo log into independent table spaces. If the rollback segment is too large due to large transaction, it is more convenient to clean up after setting

Appendix query transaction related statements

notesAll SQL statements are based on MySQL 5.7

#Query all running transactions and running time
select t.*,to_seconds(now())-to_seconds(t.trx_started) idle_time from INFORMATION_SCHEMA.INNODB_TRX t

#SQL to query transaction details and execute
select now(),(UNIX_TIMESTAMP(now()) - UNIX_TIMESTAMP(a.trx_started)) diff_sec,b.id,b.user,b.host,b.db,d.SQL_TEXT from information_schema.innodb_trx a inner join information_schema.PROCESSLIST b
on a.TRX_MYSQL_THREAD_ID=b.id and b.command = 'Sleep'
inner join performance_schema.threads c ON b.id = c.PROCESSLIST_ID
inner join performance_schema.events_statements_current d ON d.THREAD_ID = c.THREAD_ID;

#Query all historical SQL records of transaction execution
  ps.id 'PROCESS ID',
  esh.event_name 'EVENT NAME',
  esh.sql_text 'SQL',
  PERFORMANCE_SCHEMA.events_statements_history esh
  JOIN PERFORMANCE_SCHEMA.threads th ON esh.thread_id = th.thread_id
  JOIN information_schema.PROCESSLIST ps ON ps.id = th.processlist_id
  LEFT JOIN information_schema.innodb_trx trx ON trx.trx_mysql_thread_id = ps.id 
  trx.trx_id IS NOT NULL 
 #Simple query transaction lock
 select * from sys.innodb_lock_waits
 #Query transaction lock details
  c.SQL_Text blocking_sql_text,
  p.HOST blocking_host 
    r.trx_state wating_trx_state,
    r.trx_id waiting_trx_id,
    r.trx_mysql_thread_Id waiting_thread,
    r.trx_query waiting_query,
    b.trx_state blocking_trx_state,
    b.trx_id blocking_trx_id,
    b.trx_mysql_thread_id blocking_thread,
    b.trx_query blocking_query 
    information_schema.innodb_lock_waits w
    INNER JOIN information_schema.innodb_trx b ON b.trx_id = w.blocking_trx_id
    INNER JOIN information_schema.innodb_trx r ON r.trx_id = w.requesting_trx_id 
  ) tmp,
  information_schema.PROCESSLIST p,
  PERFORMANCE_SCHEMA.events_statements_current c,
  tmp.blocking_thread = p.id 
  AND t.thread_id = c.THREAD_ID 

reference resources

MySQL long transaction

Interviewer: do you know what problems big business brings and how to solve them?