Even though I didn’t go to MySQL conf this year (really sad about this), this week is gonna be most active in the community so I decided to do some community stuff too 🙂 Today I’ve released version 0.3 of our innodb recovery toolkit. Now it became much faster, stable and accurate. At this moment it is possible to recover almost any table from corrupted/deleted tablespace without so much effort as it was before. Here is a short changes list (since 0.1 announced here):
- More MySQL data types added: DECIMAL (both old and new), DATE, TIME
- CHAR data type handling improved in table definitions generator
- Indexes filtering added to page_parser
- 64-bit stat() support added to all tools
- Linux has no isnumber() function so we define our own implementation (pretty simple)
- Lots of fixes in create_defs.pl script – now it generates definitions which could recover your data in 80% cases w/o any changes.
- Min/max record size calculation fixed in constraints-based parser.
- Nullable fixed-size columns support is fixed.
- Debug logging is much cleaner now.
As always, if you need any help with your recovery, we would love to help.
We were using memcache in our application for a long time and it helped a lot to reduce DB servers load on some huge queries. But there was a problem (sometimes called a “dog-pile effect”) – when some cached value was expired and we had a huge traffic, sometimes too many threads in our application were trying to calculate new value to cache it.
For example, if you have some simple but really bad query like
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| SELECT COUNT(*) FROM some_table WHERE some_flag = X |
which could be really slow on a huge tables, and your cache expires, then ALL your clients calling a page with this counter will end up waiting for this counter to be updated. Sometimes there could be tens or even hundreds of such a queries running on your DB killing your server and breaking an entire application (number of application instances is constant, but more and more instances are locked waiting for a counter).
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How often do we think about our http sessions implementation? I mean, do you know, how your currently used sessions-related code will behave when sessions number in your database will grow up to millions (or, even, hundreds of millions) of records? This is one of the things we do not think about. But if you’ll think about it, you’ll notice, that 99% of your session-related operations are read-only and 99% of your sessions writes are not needed. Almost all your sessions table records have the same information: session_id and serialized empty session in the data field.
Looking at this sessions-related situation we have created really simple (and, at the same time, really useful for large Rails projects) plugin, which replaces ActiveRecord-based session store and makes sessions much more effective. Below you can find some information about implementation details and decisions we’ve made in this plugin, but if you just want to try it, then check out our project site.
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Last few days one of our customers (one of the largest Ruby on Rails sites on the Net) was struggling to solve some really strange problem – once upon a time they were getting an error from ActiveRecord on their site:
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| (ActiveRecord::StatementInvalid) "Mysql::Error: Lock wait timeout exceeded; try restarting transaction: UPDATE some_table..... |
They have innodb_lock_wait_timeout set to 20 seconds. After a few hours of looking for strange transactions we were decided to create s script to dump SHOW INNODB STATUS and SHOW FULL PROCESSLIST commands output to a file every 10 seconds to catch one of those moments when this error occurred.
Today we’ve got next error and started digging in our logs…
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I’m returned from my 1-week vacation today and want to say – I’ve never been so productive as I was there 😉 Blue ocean, hot sun and white sand really helped me to finish my work on the first release of one really awesome project.
Today I’m proud to announce our first public release of the Data Recovery Toolkit for InnoDB – set of tools for checking InnoDB tablespaces and recovering data from damaged tablespaces or from dropped/truncated InnoDB tables.
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