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https://issues.apache.org/jira/browse/SOLR-6137?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14019403#comment-14019403
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Steve Rowe commented on SOLR-6137:
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bq. making multiple schema API calls concurrently can block; that is, one may
get through and the other may infinite loop.
[~alexey] mentioned that problem to me a while back. IIRC this is a bug in the
optimistic concurrency implementation. I'll dig up his info and make an issue.
bq. Schema API changes return success before all cores are updated; subsequent
calls attempting to use new schema may fail
One way to fix this may be to return the schema ZK node version from Schema API
modification methods, and add a request param requiring a minimum schema ZK
node version prior to binding a schema snapshot to the request.
bq. no blocking mode should be added to schemaless... that's what the
optimistic concurrency is for.
Right, thanks Yonik, I'd forgotten optimistic concurrency's part in the
schemaless design.
> Managed Schema / Schemaless and SolrCloud concurrency issues
> ------------------------------------------------------------
>
> Key: SOLR-6137
> URL: https://issues.apache.org/jira/browse/SOLR-6137
> Project: Solr
> Issue Type: Bug
> Components: Schema and Analysis, SolrCloud
> Reporter: Gregory Chanan
>
> This is a follow up to a message on the mailing list, linked here:
> http://mail-archives.apache.org/mod_mbox/lucene-dev/201406.mbox/%3CCAKfebOOcMeVEb010SsdcH8nta%3DyonMK5R7dSFOsbJ_tnre0O7w%40mail.gmail.com%3E
> The Managed Schema integration with SolrCloud seems pretty limited.
> The issue I'm running into is variants of the issue that schema changes are
> not pushed to all shards/replicas synchronously. So, for example, I can make
> the following two requests:
> 1) add a field to the collection on server1 using the Schema API
> 2) add a document with the new field, the document is routed to a core on
> server2
> Then, there appears to be a race between when the document is processed by
> the core on server2 and when the core on server2, via the
> ZkIndexSchemaReader, gets the new schema. If the document is processed
> first, I get a 400 error because the field doesn't exist. This is easily
> reproducible by adding a sleep to the ZkIndexSchemaReader's processing.
> I hit a similar issue with Schemaless: the distributed request handler sends
> out the document updates, but there is no guarantee that the other
> shards/replicas see the schema changes made by the update.chain.
> Another issue I noticed today: making multiple schema API calls concurrently
> can block; that is, one may get through and the other may infinite loop.
> So, for reference, the issues include:
> 1) Schema API changes return success before all cores are updated; subsequent
> calls attempting to use new schema may fail
> 2) Schemaless changes may fail on replicas/other shards for the same reason
> 3) Concurrent Schema API changes may block
> From Steve Rowe on the mailing list:
> {quote}
> For Schema API users, delaying a couple of seconds after adding fields before
> using them should workaround this problem. While not ideal, I think schema
> field additions are rare enough in the Solr collection lifecycle that this is
> not a huge problem.
> For schemaless users, the picture is worse, as you noted. Immediate
> distribution of documents triggering schema field addition could easily prove
> problematic. Maybe we need a schema update blocking mode, where after the ZK
> schema node watch is triggered, all new request processing is halted until
> the schema is finished downloading/parsing/swapping out? (Such a mode should
> help Schema API users too.)
> {quote}
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