Scenario: A single version 12 server is running 100 separate databases, all started at the same time (or as fast as 100 START DATABASE statements can run), and all lightly loaded (let's say "completely idle").
Idle databases take checkpoints every 20 minutes or so, and when the 20 minutes are up all heck breaks loose, performance-wise, as all 100 databases take their checkpoints one after the other.
If something ELSE is running, say on database 101, or even some other non-database process, you can just forget latency, throughput, or whatever other measure of performance you're interested in... if the computer isn't a super-high-performer, it will be crushed for maybe a minute or two or more.
So... all I want is some method to get those 100 databases on separate checkpoint schedules, something cheaper than "upgrade the hardware".
asked 03 Jul '12, 05:31
Volker alluded to a solution in his comment to the question.... but here is the idea in more detail:
Create a database start event in each of the databases that delays a variable amount of time and then executes an explicit checkpoint. The idea is to spread the checkpoints out evenly across the ~20 minute regular checkpointing interval.
CREATE EVENT randomize_first_checkpoint TYPE DatabaseStart HANDLER BEGIN declare @num int; -- total number of databases running on server declare @ord int; -- ordinal of this database within list of databases declare @sec int; declare @min int; -- wait some time to let all databases to start (from command line!) WAITFOR DELAY '0:0:10'; -- figure out how many databases are running on the server? SELECT number as num, db_name(number) as name, number(*) as ord into #temp from sa_db_list() order by num; SET @num = ( select count(*) from #temp ); -- ... and what position is this database on the server? SET @ord = ( select ord from #temp where name = db_name() ); -- assume checkpoints occur at 20 minute regular intervals (i.e. 20*60 seconds) -- figure out how long to wait before we force a checkpoint on this database set @sec = ( 20*60 )*( @ord - 1 ) / @num; set @min = @sec / 60; set @sec = @sec - 60*@min; execute immediate 'WAITFOR DELAY ''0:' || @min || ':' || @sec || ''''; checkpoint; END;
You may want to change the initial delay in the above procedure and/or change the '20' minutes in the above computation (if you change the checkpoint interval from the default).
In case all those databases have one common DBA account (or you know all of their DBA accounts), you could also use one particular database as "checkpoint controller" and use remote database access to FORWARD CHECKPOINT statements to each database in a round-robin fashion.
That would prevent the need to alter each and every database...it would just need a remote server object - and possibly you could use one (or a few) remote servers and adapt them via ALTER SERVER USING ... on the fly:)
answered 03 Jul '12, 09:20