Replace a big hashmap in AS

Question

I have a hashmap which stores around 1 G of data is terms of key value pairs. This hashmap changes every 15 days. It will be loaded into memory and used from there.

When a new hashmap has to be loaded into the memory, there would be several transactions already accessing the hashmap in memory. How can I replace the old hashmap with the new one without effecting the current transactions accessing the old hashmap. If there a way to hot swap the hashmap in memory?

score 3 · Answer 1 · answered Jul 30 '13 at 07:04

3

Use an AtomicReference<Map<Foo, Bar>> rather than exposing a direct (hard) reference to the map. Consumers of the map will use #get(), and when you're ready to swap out the map, your "internal" code will use #set() or #getAndSet().

answered Jul 30 '13 at 07:04

Matt Ball

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Or simply mark the map volatile so that users don't have to change their code. – assylias Jul 30 '13 at 07:21
No, because you said you want to _replace_ the hashmap without effecting curring transactions accessing the old hashmap. – Matt Ball Jul 30 '13 at 14:39

assylias · Answer 2 · 2013-07-30T07:38:46.673

1

Provide a getter to the map
Mark the map private and volatile
When updating the map, create a new one, populate it and when it is ready, assign it to your private map variable.

Reference assignments are atomic in Java and volatile ensures visibility.

Caveats:

you will have two maps in memory at some stage
if some code keeps a reference to the old map it will access stale data. If that is an issue you can completely hide the map and provide a get(K key) instead so that users always access the latest map.

edited Jul 30 '13 at 07:38

answered Jul 30 '13 at 07:24

assylias

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Will ConcurrentHashMap solve my problem without having to mark it as volatile? – Abhi Jul 30 '13 at 12:22

score 0 · Answer 3 · answered Jul 30 '13 at 07:08

0

I will suggest to use caching tools like memcached if the data size is large like yours. This way you can invalidate individual items or entire cache as per your requirement.

answered Jul 30 '13 at 07:08

rai.skumar

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This is orthogonal to the OP's question. – Matt Ball Jul 30 '13 at 07:08
We have to go by in-memory solution, as the map is something which we are getting as a serialized java object from a different solution – Abhi Jul 30 '13 at 07:58

Replace a big hashmap in AS

3 Answers3