CODEWITHSUNDEEP
indexingcouchbasesql++
sriharip316
sriharip316

Reputation: 456

How couchbase ensures uniqueness of id?

As per the documentation primary index (index on document key) is optional in Couchbase. How does Couchbase efficiently ensure uniqueness of document key without an index?

Upvotes: 1

Views: 115

Answers (1)

Matthew Groves
Matthew Groves

Reputation: 26169

The primary index that documentation refers to is only for N1QL queries, and has nothing to do with enforcing uniqueness.

Instead, uniqueness is enforced by the key/value data service. From the "Data" overview documentation:

Each value (binary or JSON) is identified by a unique key, defined by the user or application when the item is saved. The key is immutable: once the item is saved, the key cannot be changed.

I am not an expert on Couchbase internals, but unique keys are fundamental to how Couchbase stores/retrieves/shards data. Check out Understanding vBuckets for more information ('vBucket' is analogous to 'shard'). Here's a snippet:

Items are written to and retrieved from vBuckets by means of a CRC32 hashing algorithm, which is applied to the item’s key, and so produces the number of the vBucket in which the item resides.

Upvotes: 1

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