information about concurrency control

Hello everyone,

I have some questions about concurrency control in mysql. I was wondering what commando do you use to check wich concurrency control you have or use in innodb. And what are the different types and security levels (for what are they protected and for what they dont give protection? And how can I raise to a higher concurrency control level?

Hopely someone can and wanne help me with this?

Greets
Matthias

Performance of large transactions and concurrency?

If I have a multi-million row table and I run a transaction that updates 50k rows, what are the performance implications of this?

Assuming it’s indexed correctly, it shouldn’t take long, but what rows are locked and how is the usage of that table affected?

  1. Are rows being updated during the transaction able to be read after the transaction starts and before it finishes?
  2. Are rows not being updated during the transaction able to be read after the transaction starts and before it finishes?
  3. If another transaction starts trying to change rows that are being changed by a previously unfinished transaction, will that transaction fail at start or after it tries to commit (assuming conflict)?

My question is for Postgres 9.3; I assume there are variations.