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From "Vyacheslav Daradur (JIRA)" <j...@apache.org>
Subject [jira] [Created] (IGNITE-10862) Introduce tool to free up space on a disc of unused memory pages
Date Wed, 09 Jan 2019 07:39:00 GMT
Vyacheslav Daradur created IGNITE-10862:

             Summary: Introduce tool to free up space on a disc of unused memory pages
                 Key: IGNITE-10862
                 URL: https://issues.apache.org/jira/browse/IGNITE-10862
             Project: Ignite
          Issue Type: Improvement
          Components: persistence
    Affects Versions: 2.7
            Reporter: Vyacheslav Daradur
             Fix For: 2.8

At the current time, Ignite is not able to release occupied disc space even if a significant
amount of data was removed from IgniteCache. It disturbs our users because they can't use
hardware effectively, also it increases TCO.


Let's imagine that we have used IgniteCache with enabled PDS during the time:
- hardware disc space has been occupied during growing up of an amount
of data, e.g. 100Gb;
- then, we removed non-actual data, e.g 50Gb, which became useless for us;
- disc space stopped growing up with new data, but it was not
released, and still took 100Gb, instead of expected 50Gb;

Another use case:
- a user extracts data from IgniteCache to store it in separate
IgniteCache or another store;
- disc still is occupied and the user is not able to store data in the
different cache at the same cluster because of disc limitation;

*Possible solutions:*

Introduce some kind of mechanics which will be able to shrink data in IgniteCache and to
free up space on a disc of mapped free memory pages.

A solution should take into account possible concurrent reads and updates of data and indexes
to maintain consistency.

Maybe, it makes sense to implement a tool to be offline at the first step that means concurrent operations
will be prohibited. 

Strongly recommended discussing design on dev-list with Ignite experts before the start of

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