# Transaction And Concurrency
+ In most cases, the database serves multiple client sessions at the same time
+ Consider the following concurrency issues when designing a database
  + `Dirty Read`: One transaction reads changes made by another uncommitted transaction
  + `Non-repeatable Read`: In a transaction, when you perform a repeat query for records later, the same query produces different results than before
  + `Phantom Read`: In a transaction, when you perform a repeat query for records later, the same query finds that new row records have appeared
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