ivankelly commented on a change in pull request #1466: Topic compaction documentation URL: https://github.com/apache/incubator-pulsar/pull/1466#discussion_r190833665
########## File path: site/docs/latest/cookbooks/compaction.md ########## @@ -0,0 +1,113 @@ +--- +title: Topic compaction cookbook +tags: [admin, clients, compaction] +--- + +Pulsar's [topic compaction](../../getting-started/ConceptsAndArchitecture#compaction) feature enables you to create **compacted** topics in which older, "obscured" entries are pruned from the topic, allowing for faster reads through the topic's history (which messages are deemed obscured/outdated/irrelevant will depend on your use case). + +To use compaction: + +* You must manually [trigger](#trigger) compaction using the Pulsar administrative API. This will both run a compaction operation *and* mark the topic as a compacted topic. +* Your {% popover consumers %} must be [configured](#config) to read from compacted topics (or else the messages won't be properly read/processed/acknowledged). + +In Pulsar, topic compaction takes place on a *per-key basis*, meaning that messages are compacted based on their key. For the stock ticker use case, the stock symbol---e.g. `AAPL` or `GOOG`---could serve as the key. + +## When should I use compacted topics? + +The classic example of a topic that could benefit from compaction would be a stock ticker topic through which {% popover consumers %} can access up-to-date values for specific stocks. On a stock ticker topic you only care about the most recent value of each stock; "historical values" don't matter, so there's no need to read through outdated data when processing a topic's messages. For topics where older values are important, for example when you need to process long series of messages in order, compaction is unnecessary and possibly even harmful. Review comment: The same topic can serve both usecases with compaction. We don't delete the old history when we compact. Compaction isn't to save space, but rather to allow clients to catch up quickly. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org With regards, Apache Git Services