Use isolation level read committed implicitly resolve concurrency conflicts

1, rc drawbacks: the emergence of non-repeatable read

Oracle non-repeatable read

Oracle lost modify

Oracle Magic Reading

update insert delete any database are plus exclusive lock

sql server select the lock (exclusive lock and a shared X is S), Oracle's select Unlock, multi-version

 

2, sql server: How to select lock issue

RR: lock until the end of the transaction.

select ...... for update: select before adding the exclusive lock, the transaction will be a plurality of transaction sequence, corresponding to a single user. (Pessimistic control model)

Short string of affairs, first submitted to obtain (positive control model)