Database – How does a SQL database handle simultaneous requests

databasedatabase-performancesql-server-2008

This may be a bit of a noob question, but I'm curious:

How can a database handle multiple simultaneous requests, most notably reads? Is every request placed in a queue, so it really occurs one at a time? Or, with a multicore processor is it possible to actually handle multiple requests at the same time?

I guess an obvious extension to this question then would be: how much does having a multiple core CPU matter to a database server?

I'm specifically thinking about MS SQL Server 2008, but this question is probably applicable to most database servers.

Best Answer

There are lots of different resources that are used to provide a database service (CPU, records on disk, memory locations, etc), and any time there's contention, yes, everything that needs to use that resource gets in line. Whenever there isn't contention (two threads on a multicore system, attempting to access different records in a table) then those requests can proceed in parallel until they contend for some resource again.

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zcat /path/to/file.sql.gz | mysql -u 'root' -p your_database

> will write the output of the mysql command on stdout into the file myfile.sql.gz which is most probably not what you want. Additionally, this command will prompt you for the password of the MySQL user "root".

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If the database is set to use the "Full" recovery mode, then you will not be able to shrink it until you have backed up the transaction logs.

If you don't require the recoverability provided by this recovery mode, set it to Simple, and you should be able to shrink the database without requiring the log backup.

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