I wrote about Galera about 1.5 years ago: State of the art: Galera – synchronous replication for InnoDB. It was about the 0.7 release, which was more like a proof-of-concept release (though Galera’s developers may not agree with that ) with some serious limitations (like using mysqldump for node propagation). The Galera team heard my suggestions and the new 0.8 release looks very promising. Well, it took 1.5 years to fix the limitations and come up with new features, but there is nothing to complain about it – a synchronous distributed transactional system is not an easy problem to solve, trust me.

So Galera 0.8 comes with many nice features:

• Works with MySQL 5.1 and MariaDB 5.1. The latest is more interesting for us, as it is based on XtraDB. That means Galera supports the XtraDB …

In the first part of this article I have showed how I align IO, now I want to share results of the benchmark that I have been running to see how much benefit can we get from a proper IO alignment on a 4-disk RAID1+0 with 64k stripe element. I haven’t been running any benchmarks in a while so be careful with my results and forgiving to my mistakes

The environment

Here is the summary of the system I have been running this on (for brevity I have removed some irrelevant information):

# Aspersa System Summary Report ##############################
    Platform | Linux
     Release | Ubuntu 10.04.2 LTS (lucid)
      Kernel | 2.6.32-31-server
Architecture | CPU = 64-bit, OS = 64-bit
# Processor …

Now that flash storage is becoming more popular, IO alignment question keeps popping up more often than it used to when all we had were rotating hard disk drives. I think the reason is very simple – when systems only had one bearing hard disk drive (HDD) as in RAID1 or one disk drive at all, you couldn’t really have misaligned IO because HDDs operate in 512-byte sectors and that’s also the smallest amount of disk IO that systems can do. NAND flash on the other hand can have a page size of 512-bytes, 2kbytes or 4kbytes (and often you don’t know what size it is really) so the IO alignment question becomes more relevant.

It was and still is, however, relevant with HDD RAID storage – technology we have been using for many years – when there’s striping like in RAID0, 5, 6 or any variation of them (5+0, 1+0, 1+0+0 etc.). While IO inside the RAID is perfectly aligned to disk sectors (again due to the fact operations are done in …

Released on June 8, 2011 (Downloads are available here and from the Percona Software Repositories.

Percona Server 5.1.57-12.8 is now the current stable release in the 5.1 series. It is is based on MySQL 5.1.57.

Bug Fixes

• Fixed InnoDB I/O code so that the interrupted system calls are restarted if they are interrupted by a signal. InnoDB I/O code was not fully conforming to the standard on POSIX systems, causing a crash with an assertion failure when receiving a signal on pwrite(). Bug Fixed: LaunchPad: #764395 / MySQL bug #60788 (A. …

One of item I always look at SHOW ENGINE INNODB STATUS to see if there are any transactions spending very long time in ACTIVE state. In the perfect world if you’re running online system you should not see transactions spending more than couple of seconds in ACTIVE state. Especially ACTIVE transactions which do not currently run any query are suspicious. There are however cases when screaming fire about ACTIVE transactions alone would be misleading. There is a whole set of applications which run quite fine while having ACTIVE measured in hours. It is JAVA applications which often run in AUTOCOMMIT=0 mode and do not explicitly commit transactions unless there were any writes. If database is configured in READ-COMMITTED transaction mode it is actually fine from performance point of view as Innodb does not have to preserve row versions going back to start of transactions.

There is however a better metric, which in most cases will …

At Percona Live last week, someone showed me a graph from their Cacti monitoring system, using the templates that I wrote. It was the buffer pool pages read, written, and created. He asked me if the graph was okay. Shouldn’t there be a lot more pages read than written, he asked? It’s a great question.

I’ve blogged before about the danger of trying to interpret ratios. Ratios are not good ways to discover whether systems are healthy. So, why graph them, then?

First, let me say that the graph actually doesn’t show a ratio — it just shows the absolute values of the reads, writes, and creates per second, stacked on top of each other. The person was mentally comparing them and creating a ratio from them. But there’s no …

MySQL 5.5 and Percona Server 5.5 do not solve all scalability problems even for read only workloads. Workloads which got a lot of attention such as Sysbench and DBT2/TPC-C scale pretty well a they got a lot of attention, there can be other quite typical workloads however which do not scale that well. This is why it is important to test performance and scalability for your application on your hardware if you really want results most relevant for your situation.

In this example I spotted the query pattern responsible for large portion of the load in the application by aggregating query log with mk-query-digest. When I filtered out only queries of this pattern and got a simplified part of production workload which focuses only on one query but yet mimics real world values distribution.

The query looks something like this:

SELECT *  FROM table WHERE deleted = 0 AND group_id IN (62715996, 62716592, 62717660, …

InnoDB compression is getting some traction, and I see quite contradictory opinions. Someone has successful deployments in productions, and someone says that compression in current implementation is useless.
To get some initial impression about performance I decided to run some sysbench with multi-tables benchmarks.
I actually was preparing to do complex research, but even first initial results are quite discouraging.

My setup: Dell PowerEdge R900, running Percona-Server-5.1.57-rel12.8 (will be in public release soon), storage is FusionIO 320GB MLC card, which does not matter a lot in this case of CPU-bound benchmark.

First stage – load data. Scripts for multi-table sysbench allow to load data in …

Few weeks ago I wrote about Innodb Caching with main idea you might need more cache when you think you are because Innodb caches data in pages, not rows, and so the whole page needs to be in memory even if you need only one row from it. I have created the simple benchmark which shows a worse case scenario by picking the random set of primary key values from sysbench table and reading them over and over again.

This time I decided to “zoom in” on the time when result drop happens – 2x increase in number of rows per step hides a lot of details, so I’m starting with some number of rows when everything was still in cache for all runs and increasing number of rows being tested 20% per step. I’m trying standard Innodb page size, 4KB page size as 16K page size compressed to 4. The data in this case compresses perfectly (all pages …

I started going over the slides from talks from MySQL Conference and Expo 2011 to pick set of must see presentations and publish the list, but this is not happening due to lack of time. Instead I’m only going to recommend 1 talk, from list of tutorials I had a chance to review. If you have not check it out yet, take a look at Linux and Hardware Optimizations by Yoshinori Matsunobu. Check out the slides which are very well done with many graphs and verbose enough explanations so you can easily follow slides alone.

Were you excited by some other talk on MySQL Conference and Expo ? Feel free to leave it as a comment to this post.