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Advanced learning of MySQL -- Fundamentals -- concurrency of transactions
2022-07-07 00:34:00 【Magic pig 9898】
What problems will occur when transactions are concurrent :
Dirty reading
A transaction reads data that has not been committed by another transaction
Explain what ?
It means that neither transaction has been committed , The data read must be inaccurate , Non persistent data .
terms of settlement :
You can make transactions concurrent
But one of the slower transactions is before reading data , You must ensure that other concurrent transactions are committed , Otherwise, it is in a state of stagnation .
be called , Read submitted .( At this time, we found that , The problem of dirty reading has been solved )
It can't be read repeatedly
In a transaction , Read the same record successively , But the data read twice is different . Call it non repeatable .
Explain what ?
Explain the business ABC Concurrent , Business A Read the transaction B Data submitted , however A Still running , also A In subsequent operation , There is another operation of reading data , But this time I read it later is C Data submitted . here A I don't understand , How can the data read be inconsistent .
terms of settlement :
Do not allow transactions that process the same data to process the data at the same time , We have to wait for the previous transaction , To allow the next transaction to proceed .
Fantasy reading
When a transaction queries a record , There is no corresponding data , But when inserting , But I can't insert it , Found that this record exists .
Explain what ?
explain , When a transaction wants to insert data into a table , Mingming originally judged that this table did not have this row of data , But it was inserted in advance by another transaction , Cause insertion failure .
terms of settlement :
Transactions that operate on the same table are not concurrent .
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