[jira] [Created] (IGNITE-10862) Introduce tool to free up space on a disc of unused memory pages

["Vyacheslav Daradur (JIRA)" <ji...@apache.org>]

Vyacheslav Daradur created IGNITE-10862:
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             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.

*Use-cases:*

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 implementation.



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