Key Value Operations
A document refers to an entry in the database (other databases may refer to the same concept as a row). A document has an ID (primary key in other databases), which is unique to the document and by which it can be located. The document also has a value which contains the actual application data. See the concept guide to Documents for a deeper dive into documents in the Couchbase Data Platform. Or read on, for a hands-on introduction to working with documents from the .NET SDK.
The core interface to Couchbase Server is simple KV operations on full documents. Make sure you’re familiar with the basics of authorization and connecting to a Cluster from the Start Using the SDK section.
Setting a Compare and Swap (CAS) value is a form of optimistic locking - dealt with in depth in the CAS page. Here we just note that the CAS is a value representing the current state of an item; each time the item is modified, its CAS changes. The CAS value is returned as part of a document’s metadata whenever a document is accessed. Without explicitly setting it, a newly-created document would have a CAS value of 0.
All of these operations involve fetching the complete document from the Cluster. Where the number of operations or other circumstances make bandwidth a significant issue, the SDK can work on just a specific path of the document with Sub-Docunent Operations.
Writes in Couchbase are written to a single node, and from there the Couchbase Server will take care of sending that mutation to any configured replicas.
durability parameter, which all mutating operations accept, allows the application to wait until this replication (or persistence) is successful before proceeding.
If no argument is provided the application will report success back as soon as the primary node has acknowledged the mutation in its memory. However, we recognize that there are times when the application needs that extra certainty that especially vital mutations have been successfully replicated, and the other durability options provide the means to achieve this.
The options differ depend on what Couchbase Server version is in use. If 6.5 or above is being used, you can take advantage of the Durable Write feature, in which Couchbase Server will only return success to the SDK after the requested replication level has been achieved. The three replication levels are:
Majority- The server will ensure that the change is available in memory on the majority of configured replicas.
MajorityAndPersistToActive- Majority level, plus persisted to disk on the active node.
PersistToMajority- Majority level, plus persisted to disk on the majority of configured replicas.
The options are in increasing levels of safety. Note that nothing comes for free - for a given node, waiting for writes to storage is considerably slower than waiting for it to be available in-memory. These trade offs, as well as which settings may be tuned, are discussed in the durability page.
If a version of Couchbase Server lower than 6.5 is being used then the application can fall-back to 'client verified' durability. Here the SDK will do a simple poll of the replicas and only return once the requested durability level is achieved.
To stress, durability is a useful feature but should not be the default for most applications, as there is a performance consideration, and the default level of safety provided by Couchbase will be reasonable for the majority of situations.
By default, Couchbase documents do not expire, but transient or temporary data may be needed for user sessions, caches, or other temporary documents.
Touch(), you can set expiration values on documents to handle transient data.
If the absolute value of the expiry is less than 30 days (such as
The value of a document can be increased or decreased atomically using
|Increment & Decrement are considered part of the ‘binary’ API and as such may still be subject to change|