Indexes in WiredTiger

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Hakan

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Sep 30, 2015, 5:10:18 PM9/30/15

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Hi all,

I want to learn a background detail about indexes in wiredTiger.

As far as I know when we create an index in MMAPv1, mmapv1 stores it in btrees data structure. My question is, does wiredTiger also store indexes in b-trees format?

Thanks.

Stephen Steneker

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Oct 5, 2015, 10:50:01 PM10/5/15

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On Thursday, 1 October 2015 07:10:18 UTC+10, Hakan wrote:

I want to learn a background detail about indexes in wiredTiger.
As far as I know when we create an index in MMAPv1, mmapv1 stores it in btrees data structure. My question is, does wiredTiger also store indexes in b-trees format?

Hi Hakan,

MongoDB (as at 3.0) only supports WiredTiger with B+ tree indexing. WiredTiger indexes also support prefix compression (enabled by default), which can reduce the footprint of both on-disk and in-memory index storage.

The underlying WiredTiger storage engine does have some features which are not exposed or supported by MongoDB yet, such as LSM (Log-Structured Merge) trees. These may be available in a future version of MongoDB, but there is still additional development required to support other configurations. For some more background on WiredTiger check out Michael Cahill’s talk from MongoDB World earlier this year: A Technical Introduction to WiredTiger.

FYI, the settings we recommend changing are exposed under storage.wiredTiger options: http://docs.mongodb.org/manual/reference/configuration-options/#storage-wiredtiger-options.