在事务中运行sql查询是否有副作用？

Question

Are there side effects running a sql select query within a transaction?

I am executing a service method which queries and inserts/updates data in one transaction block.

The query is included in the transaction. Should I expect any negative behavior from this?

Answer 1

Negative or possitive behavior is not an absolute concept.

You should design isolation and transactions according to your application needs. More isolation also longs transactions means more locks.

Answer 2

I wouldn't say there are any negative behaviors, but I know in SQL Server by default transactions lock rows. So if you have queries hitting the table you are updating/inserting into and it takes a while the queries could lock and/or timeout. You can find and example of this here .

About the select statement that is not necessarily bad if you are using it as a condition for a successful insert/update. The point of a transaction is to be able to rollback any issues if something fails. So if the query does not accomplish this goal I would leave it out of the transaction. Here's a cool article that you might want to leaf through to help you get the concept of how to use transactions effectively.

Answer 3

You will lock while the transaction is open. If you'd doing this from .NET and not careful, you will leave the lock on the table. Also, if you roll back your transaction on a table that has an identity column and insert while the first transaction is still open, you'll end up with non-contiguous identities.

However, the benefits for running things in transactions can out weigh these problems.

You should try to keep your transactions as small as possible.