What happens if you don t commit a transaction to a database say SQL Server

Question

Suppose I have a query   begin tran -- some other sql code   And then I forget to commit or roll back   If another client tries to execute a query  what would happen

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depends on the isolation level of the incomming transaction    Sql transaction isolation explained

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When you open a transaction nothing gets locked by itself  But if you execute some queries inside that transaction  depending on the isolation level  some rows  tables or pages get locked so it will affect other queries that try to access them from other transactions

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Transactions are intended to run completely or not at all  The only way to complete a transaction is to commit  any other way will result in a rollback   Therefore  if you begin and then not commit  it will be rolled back on connection close  as the transaction was broken off without marking as complete

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As long as you don t COMMIT or ROLLBACK a transaction  it s still  running  and potentially holding locks    If your client  application or user  closes the connection to the database before committing  any still running transactions will be rolled back and terminated

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You can actually try this yourself  that should help you get a feel for how this works   Open a two windows  tabs  in management studio  each of them will have it s own connection to sql    Now you can begin a transaction in one window  do some stuff like insert update delete  but not yet commit  then in the other window you can see how the database looks from outside the transaction  Depending on the isolation level  the table may be locked until the first window is committed  or you might  not  see what the other transaction has done so far  etc   Play around with the different isolation levels and no lock hint to see how they affect the results    Also see what happens when you throw an error in the transaction    It s very important to understand how all this stuff works or you will be stumped by what sql does  many a time    Have fun  GJ

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Any uncomitted transaction will leave the server locked and other queries won t execute on the server  You either need to rollback the transaction or commit it  Closing out of SSMS will also terminate the transaction which will allow other queries to execute

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The behaviour is not defined  so you must explicit set a commit or a rollback   http   docs oracle com cd B10500 01 java 920 a96654 basic htm 1003303      If auto-commit mode is disabled and you close the connection without explicitly committing or rolling back your last changes  then an implicit COMMIT operation is executed     Hsqldb makes a rollback  con setAutoCommit false   stmt executeUpdate  insert into USER values        insertedUserId       Anton   Alaf      con close      result is     2011-11-14 14 20 22 519 main            INFO   SqlAutoCommitExample 55   AutoCommit enabled   false    2011-11-14 14 20 22 546 main            INFO   SqlAutoCommitExample 65   Found 0  users in database

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Example for Transaction  begin tran tt  Your sql statements  if  error occurred      rollback tran tt else      commit tran tt  As long as you have not executed  commit tran tt   data will not be changed

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In addition to the potential locking problems you might cause you will also find that your transaction logs begin to grow as they can not be truncated past the minimum LSN for an active transaction and if you are using snapshot isolation your version store in tempdb will grow for similar reasons   You can use dbcc opentran to see details of the oldest open transaction

[sql-server] What happens if you don't commit a transaction to a database (say, SQL Server)?

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