View performance includes the time taken to update the view, the time required for the view update to be accessed, and the time for the updated information to be returned, depend on different factors. Your file system cache, frequency of updates, and the time between updating document data and accessing (or updating) a view will all impact performance.
Some key notes and points are provided below:
Index queries are always accessed from disk; indexes are not kept in RAM by Couchbase Server. However, frequently used indexes are likely to be stored in the filesystem cache used for caching information on disk. Increasing your filesystem cache, and reducing the RAM allocated to Couchbase Server from the total RAM available will increase the RAM available for the OS.
The filesystem cache will play a role in the update of the index information process. Recently updated documents are likely to be stored in the filesystem cache. Requesting a view update immediately after an update operation will likely use information from the filesystem cache. The eventual persistence nature implies a small delay between updating a document, it being persisted, and then being updated within the index.
Keeping some RAM reserved for your operating system to allocate filesystem cache, or increasing the RAM allocated to filesystem cache, will help keep space available for index file caching.
View indexes are stored, accessed, and updated, entirely independently of the document updating system. This means that index updates and retrieval is not dependent on having documents in memory to build the index information. Separate systems also mean that the performance when retrieving and accessing the cluster is not dependent on the document store.