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Priyanka
Priyanka

Reputation: 11

Hazelcast load data from RDBMS in client-server topology

I am using client-server topology for hazelcast cache. I have multiple maps which I load eagerly using MapLoaders. When there is a cache miss- Maploader's load(key) method is called. The MapLoader.load(key) method seems to be executed by the partition thread, which means that all other operations on the partition are blocked until loading is done. A very common use case for the MapLoader is to load data from a DB, which arguably can take some time. So what is the best possible approach to take so that other operations on partition are not blocked when laod is taking place? Is there any other way to load missing data at runtime?(Hazelcast version : Hazelcast 4.0.3)

Upvotes: 0

Views: 154

Answers (1)

Neil Stevenson
Neil Stevenson

Reputation: 3150

There's a good answer to this question that gives a few options.

MapLoader.load(key) only loads a single entry, but if the remote source is really slow or there are lots of cache misses it's going to mount up.

Another alternative to @mike-yawn 's answer would be to have a Runnable that fetches needed items from the database and writes them directly into the map. You can still have the MapLoader.load(key) as well, but the chances of cache miss are reduced if your fetcher code is good at predicting what entries will be needed.

If you don't cache 100% of the records, then a cache miss is inevitable. If it's punitively slow you could always return a Entry.Value that contains some sort of flag that it's a placeholder and launch a thread to do the actual load. Then your code has to deal with that placeholder and try again later -- noting that when it tries later the eventual result of the database query could be no record found.

Upvotes: 1

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