CODEWITHSUNDEEP
couchbase
Jaco van Niekerk
Jaco van Niekerk

Reputation: 745

Very frequent couchbase document updates

I'm new to couchbase and was wondering if very frequent updates to a single document (possibly every second) will cause all updates to pass through the disk write queue, or only the last update made to the document?

In other words, does couchbase optimize disk writes by only writing the document to disk once, even if updated multiple time between writes.

Based on the docs, http://docs.couchbase.com/admin/admin/Monitoring/monitor-diskqueue.html, it sounds like all updates are processed. If anyone can confirm this, I'd be grateful.

thanks

Upvotes: 3

Views: 288

Answers (2)

a4xrbj1
a4xrbj1

Reputation: 425

Jako, you should worry more about updates happening in the millisecond time frame or more than one update happening in 1 (one) millisecond. The disc write isn't the problem, Couchbase solves this intelligently itself but the fact that you will concurrency issues when you operate in the milliseconds time frame.

I've run into them fairly easily when I tested my application and first couldn't understand why Node.js (in my case) sometimes would write data to CouchBase and sometimes not. If it didn't write to CouchBase usually for the first record.

More problems raised when I first checked if a document with a specific key existed, upon not existing I would try to write it to CouchBase only to find out that in the meantime an early callback had finished and now there was indeed a key for the same document.

In those case you have to operate with the CAS flag and program it iteratively so that your app is continuously trying to pull the right document for that key and then updates. Keep this in mind especially when running tests and updates to the same document is being done!

Upvotes: 0

DaveR
DaveR

Reputation: 9640

Updates are held in a disk queue before being written to disk. If a write to a document occurs and a previous write is still in the disk queue, then the two writes will be coalesced, and only the more recent version will actually be written to disk.

Exactly how fast the disk queue drains will depend on the storage subsystem, so whether writes to the same key get coalesced will depend on how quick the writes come in compared to the storage subsystem speed / node load.

Upvotes: 4

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