[chef] Re: Effeciency of data bags?

[Joshua Timberman < >]

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Hi Mason!

On Dec 8, 2010, at 12:40 PM, Mason Turner wrote:

> I have a recipe that builds an rdist distfile by searching for nodes
> that match a particular attribute. These queries are taking about 3
> seconds, and i have less then 20 nodes in my chef DB. I'm sure there
> are some ways to optimize my chef server, but I am also considering
> pre-building the data in a databag. Does chef-client use a "last
> modified" field to prevent lookups from the databag if nothing has
> changed?


A couple hints for data bag use:

1. You can load a data bag directly rather than searching.

    mything = data_bag_item("bagname", "itemname")

Then you can access mything in your recipe.

2. You can save the data bag to the node's run_state. This is an internal 
holding area where Chef keeps track of the recipes and templates that it has 
seen, is available across all recipes in the node's run list, and is not 
persisted as a node attribute at the end of the run.

In one recipe:

    node.run_state["mything"] = data_bag_item("bagname", "itemname")

In another:

    mything = node.run_state["mything"]

We do this in the application cookbook[0], for example, to store the 
application data to use across multiple recipes.

3. (bonus) If your search query would be the same in multiple recipes (ie, 
"*:*" or similar), you can store the results in the run_state, too.

    node.run_state["nodes"] = search("node", "*:*")

[0]: http://cookbooks.opscode.com/cookbooks/application

- -- 
Opscode, Inc
Joshua Timberman, Technical Evangelist
IRC, Skype, Twitter, Github: jtimberman

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