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https://issues.apache.org/jira/browse/SOLR-12259?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16665657#comment-16665657
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Erick Erickson commented on SOLR-12259:
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[~mikemccand][~rcmuir][~jpountz][~romseygeek] I'm particularly interested in
any comments any of you have about the straw-man proposal I posted on the 24th
(and following messages).
I should reiterate that this is allowing for a one-off at-the-client's-own-risk
kind of thing, not any attempt to saddle Lucene with responsibility for
upgrades!
I think there are some minimally-intrusive things that might be added to
Lucene. In one scenario I've imagined a couple of additional interface methods
for MergePolicy that would be no-ops unless specifically needed, we will
discuss them before implementing any specifics.
The bit that worries me most is the co-existence of some custom merge policy
operating on the existing segments at the same time the merge policy configured
for normal operations was running and possibly merging. Does that problem seem
tractable to you without having to suspend indexing?
Comments?
> Robustly upgrade indexes
> ------------------------
>
> Key: SOLR-12259
> URL: https://issues.apache.org/jira/browse/SOLR-12259
> Project: Solr
> Issue Type: Improvement
> Security Level: Public(Default Security Level. Issues are Public)
> Reporter: Erick Erickson
> Assignee: Erick Erickson
> Priority: Major
>
> The general problem statement is that the current upgrade path is trappy and
> cumbersome. It would be a great help "in the field" to make the upgrade
> process less painful.
> Additionally one of the most common things users want to do is enable
> docValues, but currently they often have to re-index.
> Issues:
> 1> if I upgrade from 5x to 6x and then 7x, theres no guarantee that when I go
> to 7x all the segments have been rewritten in 6x format. Say I have a segment
> at max size that has no deletions. It'll never be rewritten until it has
> deleted docs. And perhaps 50% deleted docs currently.
> 2> IndexUpgraderTool explicitly does a forcemerge to 1 segment, which is bad.
> 3> in a large distributed system, running IndexUpgraderTool on all the nodes
> is cumbersome even if <2> is acceptable.
> 4> Users who realize specifying docValues on a field would be A Good Thing
> have to re-index. We have UninvertDocValuesMergePolicyFactory. Wouldn't it be
> nice to be able to have this done all at once without forceMerging to one
> segment.
> Proposal:
> Somehow avoid the above. Currently LUCENE-7976 is a start in that direction.
> It will make TMP respect max segments size so can avoid forceMerges that
> result in one segment. What it does _not_ do is rewrite segments with zero
> (or a small percentage) deleted documents.
> So it doesn't seem like a huge stretch to be able to specify to TMP the
> option to rewrite segments that have no deleted documents. Perhaps a new
> parameter to optimize?
> This would likely require another change to TMP or whatever.
> So upgrading to a new solr would look like
> 1> install the new Solr
> 2> execute
> "http://node:port/solr/collection_or_core/update?optimize=true&upgradeAllSegments=true";
> What's not clear to me is whether we'd require
> UninvertDocValuesMergePolicyFactory to be specified and wrap TMP or not.
> Anyway, let's discuss. I'll create yet another LUCENE JIRA for TMP do rewrite
> all segments that I'll link.
> I'll also link several other JIRAs in here, they're coalescing.
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