This is a followup to my previous post about Virtual Columns. In this post I will do a more in-depth test on using virtual columns in a use case where MariaDB is used as a document store.

Document oriented DB basics

Relational databases store data in 2-dimensional tables, rows and columns. Document oriented databases do not store Word documents or novels, rather the "documents" are essentially serialized PHP arrays, Java-objects, etc. The most popular document format today is JSON. JSON "documents" have exactly the same syntax as a JavaScript array, originally JavaScript programmers would just eval("data = " + jsondocument); to get the data into a variable (unserialize). For more …

Strangely enough, select *,colname from tbname; works just fine, whereas select colname,* from tbname; fails! So if you would like to see all columns, but have one or more of them displayed to the left of the set, you have only one way left to do it ‘comfortably’:

select colname,tbname.* from tbname; well two really but this is really the same
select colname,tb.* from tbname tb;

Because Sharing is Caring

Percona Community,

Percona Server version 5.1.51-rel11.5 is now available for download.

The main purpose of this release is to update the current Percona stable release to the latest version of MySQL 5.1.

Functionality Added or Changed

•  Percona Server 5.1.51-rel11.5 is now based on MySQL 5.1.51.
•  New Features Added: None
•  Other Changes: None

Bugs Fixed

•  Bug #661354 - Fixed a problem compiling query_cache_with comments for 5.1.51-rel11.5. (Oleg Tsarev)
•  Bug #661844 - Fixed a problem with server variables failing test for 5.1.51-rel11.5. (Oleg Tsarev)

The Release Notes for this and previous releases can be found in our …

This post continues the story started during the previous testing with MySQL 5.5.6 where I've observed a hot contention on the btr_search_latch and was curious to get a more detailed view on this performance issue.. Well, the story is starting here, but you never know what will be at the end.. ;-))

So, I've started with the same initial test workload I've before:

• dbSTRESS injector
• READ transaction: SELECT1 + SELECT2 queries
• WRITE transaction: UPDATE only queries
• think time between transactions: 0 sec.
• Concurrent user sessions: 1, 2, 4, 8, .. 256 users (growing workload)
• TPS and Query response times are collected live during all workloads..

To don't repeat again, there are just 2 links to the last graphs describing the Read-Only ( …

Recently I was forced to benchmark a mysqlnd plugin on Windows. X-Debug was no help. It worked flawless on Windows but it can’t tell you what goes on inside a PHP user space API call, for example, you will not know how much time mysqli_query() spends reading a result set. Very Sleepy is nice and the latest Microsoft Visual Studio profiler are probably wonderful but any of those external profiling tools did give me too fine-grained information. Also, they are external profiler which means you have to install extra software.

The mysqlnd statistics didn’t help me either. I didn’t need any aggregated values, I was curios if a certain function was the bottleneck. The solution:

• extra statistics for critical sections in the plugin using the mysqlnd statistics framework (C coding)
• dump profiling …

Recently I was forced to benchmark a mysqlnd plugin on Windows. X-Debug was no help. It worked flawless on Windows but it can’t tell you what goes on inside a PHP user space API call, for example, you will not know how much time mysqli_query() spends reading a result set. Very Sleepy is nice and the latest Microsoft Visual Studio profiler are probably wonderful but any of those external profiling tools did give me too fine-grained information. Also, they are external profiler which means you have to install extra software.

The mysqlnd statistics didn’t help me either. I didn’t need any aggregated values, I was curios if a certain function was the bottleneck. The solution:

• extra statistics for critical sections in the plugin using the mysqlnd statistics framework (C coding)
• dump profiling …

Leading up to my previous post, I had been doing some work to start the integration of PERFORMANCE_SCHEMA data with MySQL Enterprise Monitor, including some new graphs based on some of the data that I talked about in the above post..

A picture tells a thousand words:

This is only scratching the surface - more to come, watch this space!

Share and Enjoy:

…

Recently I happen to install MySQL on Mac OS X (Darvin Kernel).  Below are the quick 5 steps to accomplish the task. Step 1: Check Mac Version Very first step…

The post Installing MySQL On Mac OS X (Darwin Kernel) first appeared on Change Is Inevitable.

Mark Callaghan over at Facebook wrote a note recently about InnoDB disk IO counters in SHOW STATUS, with some extra things that he wanted to track. I posted a quick comment over there, but I thought this deserved it’s own write up.

MySQL 5.5’s PERFORMANCE_SCHEMA has had a fair bit written about it in terms of tracking synchronization point contention (mutexes etc.), but it currently tracks two orders within the wait class - these are /wait/synch and /wait/io.

Actually, allow me to detour first, it’s not clear from the documentation, though it is clear in the worklog. Each …

Every once in a while, we hear of users with corruption in a file system that sits on top of DRBD. That may be easy or tricky to resolve. If you’re lucky, a simple fsck will resolve the corruption. If you’re not quite that lucky, you may have to get out your backups.

But that’s typically not DRBD’s fault. Typically not at all, not in the least bit. DRBD is a block device, and as such it has no idea what rests on top of it. It has no concept of a filesystem, let alone its integrity. That of course is true for any other block device as well. If you have, say, RAID-1, and something corrupts the file system on top of it, then of course that corruption will be happily replicated across both component devices. DRBD is no different, except that its component devices are stored across distinct physical nodes.

And even if everything about your filesystem is logically correct, there’s still the chance that a …