The concurrency tag has no wiki summary.
4
votes
2answers
3k views
Using multiple cores for single MySQL queries on Debian
I am running a MySQL server for tests on a VM (VMWare) with Debian as guest OS. The guest has four emulated CPU cores, so I set thread_concurrency to four.
I am doing expensive joins on large tables, ...
3
votes
2answers
498 views
Concurrently update with limit mysql
I want to know if concurrently UPDATE .... LIMIT N will not overlap with more than one client querying the db.
After UPDATE ... LIMIT N the client will make a SELECT with some client_id assigned.
I ...
20
votes
4answers
737 views
How do you test for race conditions in a database?
I try to write database code to make sure that it's not subject to race conditions, to make sure that I've locked the correct rows or tables. But I often wonder: Is my code correct? Is it possible to ...
13
votes
3answers
1k views
Managing concurrency when using SELECT-UPDATE pattern
Let's say you have the following code (please ignore that it's awful):
BEGIN TRAN;
DECLARE @id int
SELECT @id = id + 1 FROM TableA;
UPDATE TableA SET id = @id; --TableA must have only one row, ...
7
votes
4answers
794 views
Locking issue with concurrent DELETE / INSERT in PostgreSQL
This is pretty simple, but I'm baffled by what PG does (v9.0).
We start with a simple table:
CREATE TABLE test (id INT PRIMARY KEY);
and a few rows:
INSERT INTO TEST VALUES (1);
INSERT INTO TEST ...
3
votes
2answers
412 views
SQL Server (2012) non-blocking DDL?
I'm not very experienced with SQL Server, so maybe I'm missing something
My situation is as follows:
Session 1 runs a CREATE TABLE (or other CREATE statements) with autocommit off and the CREATE is ...
2
votes
1answer
281 views
performance issues when concurrent requests
We are using SQL Server 2008 R2 on a Windows Server 2008 server.
We have some main functions which uses some Stored Procedures which has a lot of sub-queries inside of it.
I'll take one SP as an ...
0
votes
1answer
189 views
Show processlist / Max concurrent connections seem to max out at 131
When I put my database under a load test (basically just a basic write and basic read from our app), and run show processlist; in the middle of it, there is always 131 rows in the set and that's it. ...
