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From Erick Erickson <erickerick...@gmail.com>
Subject Re: SolrCloud replicas consistently out of sync
Date Mon, 16 May 2016 16:02:26 GMT
8 nodes, 4 shards apiece? All in the same JVM? People have gotten by
the GC pain by running in separate JVMs with less Java memory each on
big beefy machines.... That's not a recommendation as much as an
observation.

That aside, unless you have some very strange stuff going on this is
totally weird. Are you hitting OOM errors at any time you have this
problem? Once you hit an OOM error, all bets are off about how Java
behaves. If you are hitting those, you can't hope for stability until
you fix that issue. In your writeup there's some evidence for this
when you say that if you index multiple docs at a time you get
failures.

Do your Solr logs show any anomalies? My guess is that you'll see
exceptions in your Solr logs that will shed light on the issue.

Best,
Erick

On Mon, May 16, 2016 at 8:03 AM, Stephen Weiss <Steve.Weiss@wgsn.com> wrote:
> Hi everyone,
>
> I'm running into a problem with SolrCloud replicas and thought I would ask the list to
see if anyone else has seen this / gotten past it.
>
> Right now, we are running with only one replica per shard.  This is obviously a problem
because if one node goes down anywhere, the whole collection goes offline, and due to garbage
collection issues, this happens about once or twice a week, causing a great deal of instability.
 If we try to increase to 2 replicas per shard, once we index new documents and the shards
autocommit, the shards all get out of sync with each other, with different numbers of documents,
different numbers of documents deleted, different facet counts - pretty much totally divergent
indexes.  Shards always show green and available, and never go into recovery or any other
state as to indicate there's a mismatch.  There are also no errors in the logs to indicate
anything is going wrong.  Even long after indexing has finished, the replicas never come back
into sync.  The only way to get consistency again is to delete one set of replicas and then
add them back in.  Unfortunately, when we do this, we invariably discover that many documents
(2-3%) are missing from the index.
>
> We have tried setting the min_rf parameter, and have found that when setting min_rf=2,
we almost never get back rf=2.  We almost always get rf=1, resend the request, and it basically
just goes into an infinite loop.  The only way to get rf=2 to come back is to only index one
document at a time.  Unfortunately, we have to update millions of documents a day and it isn't
really feasible to index this way, and even when indexing one document at a time, we still
occasionally find ourselves in an infinite loop.  This doesn't appear to be related to the
documents we are indexing - if we stop the index process and bounce solr, the exact same document
will go through fine the next time until indexing stops up on another random document.
>
> We have 8 nodes, with 4 shards a piece, all running one collection with about 900M documents.
 An important note is that we have a block join system with 3 tiers of documents (products
-> skus -> sku_history).  During indexing, we are forced to delete all documents for
a product prior to adding the product back into the index, in order to avoid orphaned children
/ grandchildren.  All documents are consistently indexed with the top-level product ID so
that we can delete all child/grandchild documents prior to updating the document.  So, for
each updated document, we are sending through a delete call followed by an add call.  We have
tried putting both the delete and add in the same update request with the same results.
>
> All we see out there on Google is that none of what we're seeing should be happening.
>
> We are currently running Solr 6.0 with Zookeeper 3.4.6.  We experienced the same behavior
on 5.4 as well.
>
> --
> Steve
>
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