[HBASE-4102] atomicAppend: A put that appends to the latest version of a cell; i.e. reads current value then adds the bytes offered by the client to the tail and writes out a new entry

• Type: New Feature
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 0.94.0
• Hadoop Flags: Reviewed
• Assignee: Lars Hofhansl
• Reporter: Michael Stack
• Created: 15/Jul/11 00:17
• Updated: 12/Oct/12 05:34
• Resolved: 12/Oct/11 21:43

Description

Its come up a few times that clients want to add to an existing cell rather than make a new cell each time. At our place, the frontend keeps a list of urls a user has visited – their md5s – and updates it as user progresses. Rather than read, modify client-side, then write new value back to hbase, it would be sweet if could do it all in one operation in hbase server. TSDB aims to be space efficient. Rather than pay the cost of the KV wrapper per metric, it would rather have a KV for an interval an in this KV have a value that is all the metrics for the period.

It could be done as a coprocessor but this feels more like a fundamental feature.

Benoît suggests that atomicAppend take a flag to indicate whether or not the client wants to see the resulting cell; often a client won't want to see the result and in this case, why pay the price formulating and delivering a response that client just drops.