CODEWITHSUNDEEP
mongodb
meawoppl
meawoppl

Reputation: 2802

Mongo _id Insert Uniqueness Check

I have a medium to large Mongo collection containing image metadata for >100k images. I am generating a UUID for each image generated and using it as the _id field in the imageMeta.insert() call.

I know for a fact that these _id's are unique, or at least as unique as I can expect from boost's UUID implementation, but as the collection grows larger, the time to insert a record has grown as well.

I feel like to ensure uniqueness of the _id field Mongo must be double-checking these against the other _ids in the database. How is this implemented, and how should I expect the insert time to grow wrt. to the collection size?

Upvotes: 0

Views: 129

Answers (1)

JRP
JRP

Reputation: 989

The _id field in mongo is required to be unique and indexed. When an insert is performed, all indexes in the collection are updated, so it's expected to see insert time increase with the number of indexes and/or documents. Namely, all collections have at least one index (on the _id field), but you've likely created indexes on fields that you frequently query, and those indexes also get updated on every insert (adding to the latency).

One way to reduce perceived database latency is to specify a write concern to your driver. Note that the default write concern prior to November 2012 was 'unacknowledged', but it has since been changed to 'acknowledged'.

Upvotes: 2

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