sql deadlock

avoids Phantom reads, and how does it happen? Of course we need to use the lock! Execute on Transaction A: Update msg set message= ' order ' where token= ' ASD '; InnoDB will first add an X lock to the records on the index, as well as the RC level, plus a lock on the non-unique index ' ASD ' with the interval of the adjacent two indexes . This way, when transaction B is executed, insert into MSG values (null, ' ASD ', ' hello '); Commit, the first check whether the interval is locked, if locked

by the deadlock statement;Lockwait: The state of the deadlock if there is a content representation being deadlocked.Status: State, active indicates deadlockMachine: The device where the deadlock statement resides.Program: The main application that generated the deadlock statement.2) You can view the

, such as select .. for update limit, when other servers execute the same SQL statement, they will automatically wait for the release lock. after the previous server lock is released, the server will be able to query the next 30 data records. If more intelligence is required, oracle supports for update skip locked to skip the lock area, so that the next 30 records that are not locked can be queried immediately without waiting. The following describes

the deadlock, if there is content to indicate a deadlock.Status: State, active indicates deadlockMachine: The machine where the deadlock statement resides.Program: Which application is the main source of the statement that generated the deadlock.2 Execute the following statement with the DBA user to view the statement that is deadlocked.Select Sql_text from V$

still be operated. Such a server, such as select .. for update limit, when other servers execute the same SQL statement, they will automatically wait for the release lock. after the previous server lock is released, the server will be able to query the next 30 data records. If more intelligence is required, oracle supports for update skip locked to skip the lock area, so that the next 30 records that are not locked can be queried immediately without

Label:If there are two sessions, each session holds the resources that another session wants, and a deadlock occurs.The following experiments are used to illustrate the causes and solutions of deadlocks.SESSION1:Sql> CREATE TABLE t2 as SELECT * from EMP;Sql> select * from T2 where empno=7369;EMPNO ename JOB MGR hiredate SAL COMM DEPTNO---------- ---------- ------

Background knowledge:MySQL has three levels of Lock: page level, table level, row level.The MyISAM and memory storage engines use table-level locks (table-level locking), BDB storage engines use page locks (page-level locking), but table-level locks are also supported The InnoDB storage engine supports both row-level locks (row-level locking) and table-level locks, but row-level locks are used by default.MySQL features of these 3 types of locks can be broadly summarized as follows:Table-level Lo

database user used by the deadlock statement;Lockwait: The state of the deadlock if there is a content representation being deadlocked.Status: State, active indicates deadlockMachine: The device where the deadlock statement resides.Program: The main application that generated the deadlock statement.2) You can view the

In today's article I want to talk about the 2 types of deadlocks that can be caused when you run a transaction in the repeatable read isolation level (Transaction isolation levels repeatable Read) . When you use the repeatable read (REPEATABLE Read) isolation level to set up your transaction, SQL Server takes a shared lock on the read data hold (shared Locks) until the end of the transaction (commit or Rollbak). Then when you try to modify the read da

for A Thread 1 waits for thread 2, thread 2 waits for thread 3, thread 3 waits for thread 4, thread 4 waits for thread 1. Deadlock in Database More complicated deadlock scenarios occur in database transactions. A database transaction may consist of multiple SQL update requests. When a record is updated in a transaction, the record is locked to avoid update req

Label: --Deadlock Query statement Select bs.username "Blocking user", bs.username "DB user", Ws.username "Waiting User", BS. Sid "Sid", WS. SID "Wsid", bs.serial# "serial#", bs.sql_address "address", Bs.sql_hash_value "SQL Hash", bs.program "Blocking App", Ws.program "Waiting App", bs.machine "Blocking machine", Ws.machine "Waiting Machine", Bs.osuser "Bl

deadlock.2 Execute the following statement with the DBA user to view the statement that is deadlocked.Select Sql_text from V$sql where Hash_value in(select Sql_hash_value from v$session where SID in(select session_id from V$locked_object)) Four, deadlock resolution methodIn general, as long as the statement that will produce the

indicate a deadlock.Status: State, active indicates deadlockMachine: The machine where the deadlock statement resides.Program: Which application is the main source of the statement that generated the deadlock.2 Execute the following statement with the DBA user to view the statement that is deadlocked.Select Sql_text from V$sql where Hash_value in(select Sql_hash

indexes) brought by level two indexes. You can refer to the analysis here: http://hedengcheng.com/?p=771 4, business less use or no lock in share mode, for update such a display lock, and should try to take the snapshot read. 5, write SQL, pay attention to use the Explain Command analysis execution plan, can walk Index walk index, can walk overlay index (avoid query unnecessary column). But there is no more useful

% ' select count ( 0 ) from fn_trace_gettable ( ' F: \ perfmon \ trace_xxxx_20110406a.trc ' , default ) where textdata like ' %@ smessage varchar (8000), @ sinmaterecid varchar (18), @ srefrecid varchar (8000) % ' The number of deadlocks in a day is about 20, and there is only one record at the update, but why is there such a frequent deadlock? Besides the large data volume of the tableIn addition to super a