1
vote
1answer
36 views

Is it possible that records are changed while a read query is still executing?

Suppose a read (select) query R is reading some 100 records from a table, 50 records are read so far, could in the meanwhile a write query W change some of the unread records? We didn't take any ...
1
vote
1answer
44 views

MySQL consistent nonlocking reads vs. INSERT … SELECT

So, from my reading of the MySQL 5.5 documentation and some experiments I did with colleagues, I understand that the following is the case: With InnoDB tables, a simple SELECT statement (one that ...
2
votes
1answer
83 views

Does READ UNCOMMITTED have the same effect as AUTOCOMMIT=1?

AFAIK running transactions as READ UNCOMMITTED means that there is no lock, so every change caused by a transaction is immediately visible to other transactions. Is it correct to assume that this is ...
2
votes
1answer
121 views

What is the standard isolation level for a db used for money data?

When using a database server for monetary/financial data, I can only assume that using transactions is mandatory. But what I am not sure is which is usually the isolation level? Is a READ-REPEATABLE ...
0
votes
0answers
67 views

MySQL server vs client isolation levels

What is the difference between setting the transaction isolation level in the client configuration and the server configuration? If I set the client isolation level to be serializable while the ...
3
votes
1answer
776 views

Why can't I change the isolation levels of my connection in MySQL?

I am trying to experiment a bit with the isolation level of MySQL in a test environment. I do the following: mysql> set @@session.tx_isolation='READ-UNCOMMITED'; ERROR 1231 (42000): Variable ...
0
votes
0answers
94 views

What would this non-'unique index with a unique search condition` query lock?

I am not sure about this part of the transaction manual For locking reads (SELECT with FOR UPDATE or LOCK IN SHARE MODE), UPDATE, and DELETE statements, locking depends on whether the statement ...
6
votes
4answers
2k views

MySQL InnoDB locks primary key on delete even in READ COMMITTED

Preface Our application runs several threads that execute DELETE queries in parallel. The queries affect isolated data, i.e. there should be no possibility that concurrent DELETE occurs on the same ...