One of the most typical reasons for performance and scalability problems I encounter is simply failing to do the math. And these are typically… or more when it previously took seconds. So what math would be in the case like this ? Say you have query like… DESC LIMIT 100″ to find the most visited pages as a simple example. Before you can do the math (or say apply mathematical model…
Post: The MySQL optimizer, the OS cache, and sequential versus random I/O
April 28, 2008 By 17 Comments
… disk can do about 100 random I/O’s per second, as a rule of thumb. If you do the math with the rows column in EXPLAIN, you realize that this equates to about 18790 * 606 = 11386740 I/O operations, assuming that the… slow. Now let’s look at the alternative: table-scan the fact table, and do index lookups in the two dimension tables. MySQL doesn…
Post: How to estimate query completion time in MySQL
April 22, 2008 By 14 Comments
… of the simplest is to estimate how many rows the query needs to examine, measure how fast it’s working, and do the math. As… per second, and there were 150 million rows in the table. A little math later, and you get 3488 seconds to completion, or a little less than an hour. And indeed the query completed…
Post: Aligning IO on a hard disk RAID – the Theory
June 9, 2011 By 15 Comments
… of the other three disks instead of just doing one IO to each of the disks. In this case even if this is the… a manual on your system to be sure you’re doing the right thing. Say we have 6-disk RAID5 (so 5… make sure you’re using sectors as units to simplify the math. Besides DOS partition table which you would typically work with using…
Post: Rendundant Array of Inexpensive Servers
August 21, 2008 By 15 Comments
… and recovery of the slave is very easy and causes no business impact. This is fine assuming you do the math and the performance gains…. Even if you do not have spare hard drive you can often pool the one from the spare server and have the “warranty man… from this angle it may be justified only for the most critical servers. Do not forget redundant power supplies also increase server…
Comment: Choosing innodb_buffer_pool_size
April 15, 2010 By 38 Comments
… on my tables. Without any MyISAM tables I would change the buffer pool somewhere in between 8-10 G (probably closer…’m careful like that). Paul, Completely depends on what you do with the database, and if you have MyISAM as well. You… it at 1.5 G, although you will have to do the math to see how many connections you have at once and…
Post: Traffic Tricks by Hosting Providers.
October 17, 2007 By 13 Comments
… firewall or something similar – they told me they do not. Looking closer at the problem I discovered my NIC is now switched…. Now I’m given the option to unblock it in the control panel manually but I have to do this each 250GB of… hours. And that was not even in the fine print. The funnies thing is if you do the math here – if you use 5Mbit/Sec…
Post: The case for getting rid of duplicate “sets”
May 17, 2011 By 2 Comments
… up the number one 10 times, and then then ten times more? Of course not. You did simple arithmetic to make the math… compression for the other attributes. Don’t use FLOAT with this method (don’t use it at all). We can do even… original relation before compression? This is a way to do it without using the “search set” trick above. Also, notice that it…
Comment: Funniest bug ever
February 10, 2009 By 19 Comments
… the same scenarios). Now suppose that you’re accessing them all randomly; you can do the math at how many times you’ll be doing…’t seen significant performance changes from adding noatime,nodiratime to the mount options on “normal” servers with a few hundred tables. You can change the mount options at runtime so it’s pretty easy to…
Comment: Just do the math!
July 8, 2009 By 4 Comments
You would be surprised how controversial “doing the math” is. To most the database is supposed to magically compensate for whatever you throw at it regardless of how its configured or your data model is designed. Saying otherwise is well, “being mean”.
