[
https://issues.apache.org/jira/browse/LUCENE-3569?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13146984#comment-13146984
]
Shai Erera commented on LUCENE-3569:
------------------------------------
{code}
i dont like pushing optimize-type merging into an MP, because then
its settable in IWConfig (as the regular MP).
{code}
So? I have a code path which opens an IndexWriter just to run index
optimization and closes it. The thing is - it's the user who sets the MP, and
if he wants to set an MP that always does optimize, why should we block him? If
the MP's name is clear enough that this is a devastating thing to do
'regularly' then isn't it the user's decision whether to set it or not?
We cannot really prevent it - someone could write a 'regular' MP that always
optimizes. The changes in this issue propose to remove the distinction between
optimize, maybeMerge and expungeDeletes. You do index maintenance and you
define what maintenance you'd like to do through the maintenance policy
(however we'll end up calling it).
> Consolidate IndexWriter's optimize, maybeMerge and expungeDeletes under one
> merge(MP) method
> --------------------------------------------------------------------------------------------
>
> Key: LUCENE-3569
> URL: https://issues.apache.org/jira/browse/LUCENE-3569
> Project: Lucene - Java
> Issue Type: Improvement
> Components: core/index
> Reporter: Shai Erera
>
> Today, IndexWriter exposes 3 methods for 'cleaning up' / 'compacting' /
> 'optimizing' your index:
> * optimize() -- merges as much segments as possible (down to 1 segment), and
> is discouraged in many cases because of its performance implications.
> * maybeMerge() -- runs 'subtle' merges. Attempts to balance the index by not
> leaving too many segments, yet not merging large segments if unneeded.
> * expungeDeletes() -- cleans up deleted documents from segments and on the go
> merges them.
> * a default MP that can be set on IndexWriterConfig, for ongoing merges IW
> performs (i.e. as a result of flushing a new segment).
> These methods are confusing in several levels:
> * Their names are misleading, see LUCENE-3454.
> * Why does expungeDeletes need to merge segments?
> * Eventually, they really do what the MergePolicy decides that should be
> done. I.e., one could write an MP that always merges all segments, and
> therefore calling maybeMerge would not be so subtle anymore. On the other
> hand, one could write an MP that never merges large segments (we in fact have
> several of those), and therefore calling optimize(1) would not end up with
> one segment.
> So the proposal is to replace all these methods with a single one
> merge(MergePolicy) (more on the names later). MergePolicy will have only one
> method findSegmentsForMerge and the caller will be responsible to configure
> it in order to perform the needed merges. We will provide ready-to-use MPs:
> * LightMergePolicy -- for setting on IWC and doing the ongoing merges IW
> executes. This one will pick segments respecting various parameters such as
> mergeFactor, segmentSizes etc.
> * HeavyMergePolicy -- for doing the optimize()-style merges.
> * ExpungeDeletesMergePolicy -- for expunging deletes (my proposal is to drop
> segment merging from it, by default).
> Now about the names:
> * I think that it will be good, API-backcompat wise and in general, if we
> name that method doMaintenance (as expungeDeletes does not have to merge
> anything).
> * Instead of MergePolicy we call it MaintenancePolicy and similarly its
> single method findSegmentsForMaintenance, or getMaintenanceSpecification.
> * I called the MPs Light and Heavy just for the text, I think a better name
> should be found, but nothing comes up to mind now.
> It will allow us to use this on 3.x, by deprecating MP and all related
> methods.
--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators:
https://issues.apache.org/jira/secure/ContactAdministrators!default.jspa
For more information on JIRA, see: http://www.atlassian.com/software/jira
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
