[jira] [Created] (SOLR-12941) IndexSizeTrigger and splitMethod=link problems

["Andrzej Bialecki (JIRA)" <ji...@apache.org>]

Andrzej Bialecki  created SOLR-12941:
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             Summary: IndexSizeTrigger and splitMethod=link problems
                 Key: SOLR-12941
                 URL: https://issues.apache.org/jira/browse/SOLR-12941
             Project: Solr
          Issue Type: Bug
      Security Level: Public (Default Security Level. Issues are Public)
    Affects Versions: 7.6, master (8.0)
            Reporter: Andrzej Bialecki 
            Assignee: Andrzej Bialecki 


{{IndexSizeTrigger}} can be configured to use {{splitMethod=link}} (SOLR-12730), which uses hard-linking for creating sub-shards.

However, if the trigger uses {{aboveBytes}} condition the resulting sub-shards will not immediately decrease in size, until all of the deleted documents will be expunged (either by gradual merges or by explicit and costly expungeDeletes command). As a result the new sub-shards will still exceed the {{aboveBytes}} threshold, which will cause the trigger to keep generating new split requests.

I see two options how to solve this:
 * disallow using {{aboveBytes}} with {{splitMethod=link}}. This unfortunately is a very desirable combination because it monitors the actual index size and uses the fast splitting method.
 * calculate an internal estimate of "eventual index size" for an index with deletions, and use this estimate when checking with {{aboveBytes}} instead of the real index size. This of course introduces a potentially significant estimation error but allows to properly treat hard-linked sub-shards with deletions as (eventually) significantly smaller than the parent shard.



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