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.
If you’ve ever worked in companies with 5-10+ servers and it was your responsibility to install new boxes, change some configuration files and install new software on many boxes you definitely know how painful this work is. Every time you need to change something on 3-5-100 boxes, you go there and make those changes. Most experienced of us used some weird scripts to perform some task on many boxes or used some stuff like dsh. Even with those tricks I’d never wish this work to anyone.
While I was working in Galt, I’ve asked our junior admin to check out puppet and try to use it on our servers. After a week of screaming he’s managed to install and configure it and said “Wow! This is what we definitely need!”. Since then he was using it and was happy :-). But, unfortunately (for me) I’ve never tried it and when I’ve changed my job and started doing the same old (but not good) things like dsh and for+ssh I’ve started thinking: “Stop! Try puppet – maybe it is what you need!”. And what can i say? Yes! This is what every admin needs! Today we’ve deployed our next web server (we do it pretty often) and it was done with puppet – pretty painlessly and quickly.
So, what is puppet? Let me quote their site:
Puppet lets you centrally manage every important aspect of your system using a cross-platform specification language that manages all the separate elements normally aggregated in different files, like users, cron jobs, and hosts, along with obviously discrete elements like packages, services, and files.
Puppet’s simple declarative specification language provides powerful classing abilities for drawing out the similarities between hosts while allowing them to be as specific as necessary, and it handles dependency and prerequisite relationships between objects clearly and explicitly. Puppet is written entirely in Ruby.
Basically, puppet is a tool which lets you describe whatever you’d like about your server(s) and deploy your configuration (configs, packages, files, directories, cron jobs, user accounts, ssh keys, etc) to any number of servers you need. You can describe some simple parts of your system (like “apache”, “nginx”, “rails”, “useful_gems”, “admin-ssh-keys”, etc) and then describe your servers using those terms (like machine X = apache+rails+useful_gems+admin_ssh_keys). When it is done, you’ll be able to deploy all this stuff with one command!
So, if you’re struggling with deploying some changes on many servers or, even, have only a few of them, I’d recommend to try puppet – it could save you a lots of time and nerves.
P. S. When you’ll try to use it – do not give up for a few days – it is hard to change your way of thinking and start writing correct and convenient scripts using puppet’s language.
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
1
| 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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This will be one of those posts I’d like to publish primarily to be able to coma back later and check it out instead of reading docs again 🙂
So, we have a server with two (or more) network interfaces are we need to be able to use more than one interface in our VDS machines. How do we set it up?
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