CouchDB .view file growing out of control?

Question

I recently encountered a situation where my CouchDB instance used all available disk space on a 20GB VM instance. Upon investigation I discovered that a directory in /usr/local/var/lib/couchdb/ contained a bunch of .view files, the largest of which was 16GB. I was able to remove the *.view files to restore normal operation. I'm not sure why the .view files grew so large and how CouchDB manages .view files.

A bit more information. I have a VM running Ubuntu 9.10 (karmic) with 512MB and CouchDB 0.10. The VM has a cron job which invokes a Python script which queries a view. The cron job runs once every five minutes. Every time the view is queried the size of a .view file increases. I've written a job to monitor this on an hourly basis and after a few days I don't see the file rolling over or otherwise decreasing in size.

Does anyone have any insights into this issue? Is there a piece of documentation I've missed? I haven't been able to find anything on the subject but that may be due to looking in the wrong places or my search terms.

Answer 1

CouchDB is very disk hungry, trading disk space for performance. Views will increase in size as items are added to them. You can recover disk space that is no longer needed with cleanup and compaction.

Every time you create update or delete a document then the view indexes will be updated with the relevant changes to the documents. The update to the view will happen when it is queried. So if you are making lots of document changes then you should expect your index to grow and will need to be managed with compaction and cleanup.

If your views are very large for a given set of documents then you may have poorly designed views. Alternatively your design may just require large views and you will need to manage that as you would any other resource.

It would be easier to tell what is happening if you could describe what document updates (inc create and delete) are happening and what your view functions are emitting, especially for the large view.

Answer 2

That your .view files grow, each time you access a view is because CouchDB updates views on access. CouchDB views need compaction like databases too. If you have frequent changes to your documents, resulting in changes in your view, you should run view compaction from time to time. See http://wiki.apache.org/couchdb/HTTP_view_API#View_Compaction

To reduce the size of your views, have a look at the data, you are emitting. When you emit(foo, doc) the entire document is copied to the view to it is very instantly available when you query the view. the function(doc) { emit(doc.title, doc); } will result in a view as big as the database itself. You could also emit(doc.title, nil); and use the include_docs option to let CouchDB fetch the document from the database when you access the view (which will result in a slightly performance penalty). See http://wiki.apache.org/couchdb/HTTP_view_API#Querying_Options