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https://issues.apache.org/jira/browse/SOLR-17460?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17897305#comment-17897305
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Arda commented on SOLR-17460:
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[~epugh] Thank you for asking! That’s a great question. There were two main
reasons behind the decision to migrate from Solr 7 to Solr 8 before moving to
Solr 9:
*1. Dependency Considerations:* Some of the other products that collaborate
with the Solr environment have recommended using Solr 8 for compatibility
reasons, even though it’s not strictly necessary, but preferred. Because of
this, I think, sticking with Solr 8 ensures better alignment and helps maintain
stability across these integrations, which minimizes any potential
interruptions.
*2. Risk Mitigation:* Jumping straight from Solr 7 to Solr 9 means skipping
over a major version (Solr 8), and with that comes major changes. I think, it
may provide serious risks to a production environment. By upgrading
step-by-step, I can manage any compatibility and configuration changes
gradually, reducing the risk of serious issues along the way.
Before moving on to Solr 9, I can fully test and resolve any issues by
upgrading to Solr 8.
> Error During Collection Migration from Solr 7.0 to Solr 8.4: Missing Files
> and Shard Restoration Failures
> ---------------------------------------------------------------------------------------------------------
>
> Key: SOLR-17460
> URL: https://issues.apache.org/jira/browse/SOLR-17460
> Project: Solr
> Issue Type: Bug
> Components: hdfs, SolrCloud
> Affects Versions: 7.0, 8.4
> Reporter: Arda
> Priority: Minor
> Labels: backup, restore
>
> I was attempting to migrate a collection with 3 shards from a Solr 7.0
> cluster to a Solr 8.4 cluster. The data is stored in HDFS. I followed the
> backup-restore process but encountered issues with two of the shards during
> the restoration.
> h1. *Migration Process:*
> *1-* *Backup Command:* To avoid timeouts, I initiated the backup with an
> async parameter:
> curl -k --negotiate -u :
> 'https://<solrNode>:<solrPort>/solr/admin/collections?action=BACKUP&name=<backupName>&collection=<solrCollectionName>x&location=<hdfsPath>&
> async=12346'
> *2- Copy Backup to Local:* After the backup, I copied the data from HDFS to
> the local filesystem:
> hdfs dfs --copyToLocal <backupPath> <localPath>
> *3- Transfer Backup to New Cluster:* I then copied the backup files from the
> older Solr node to the newer one:
> scp -pr <localPath> <username>@<ip>:<localPathDestination>
> *4- Prepare New HDFS Path:* On the new Solr cluster, I created a new
> directory in HDFS and adjusted ownership:
> hdfs dfs -mkdir <pathName2>
> hdfs dfs -chown solr:solr <pathName2>
> *5- Copy Backup to New HDFS Location:* I transferred the backup data from
> local to the new HDFS path. Before that, I deleted
> "<str>queryDocAuthorization</str>" parts from solrconfig.xml file to become
> compatible with the newer version.
> hdfs dfs --copyFromLocal <localPathDestination> <pathName2>
> *6- Restore Collection:* Finally, I ran the restore command:
> curl -k --negotiate -u :
> 'https://<solrNode>:<solrPort>/solr/admin/collections?action=RESTORE&name=<backupName>&collection=<solrCollectionName>x&location=<hdfs_path>&
> async=12345'
> h1.
> *Issue:*
> After the restore process completed, I found that two of the shards could not
> be restored. The logs displayed the following errors:
> *Error During Shard Restoration:*
> ERROR [c: <solrCollectionName> s: shard2 r:core_node5 x: :
> <solrCollectionName>_shard2_replica_n4] o.a.s.h.RequestHandlerBase
> org.apache.solr.common. SolrException: Error CREATEing SolrCore
> '<solrCollectionName>_shard2_replica_n4': Unable to create core
> [:<solrCollectionName>_shard2_replica_n4] Caused by:
> org.apache.solr.handler.component.QueryDocAuthorizationComponent.....
> *FileNotFoundException and Index Corruption:*
> WARN
> (parallelCoreAdminExecutor-6-thread-7-processing-n:<solrNode>:<solrPort>_solrx:<solrCollectionName>_shard2
> _replica_n1 <numbers> RESTORECORE) [x:<solrCollectionName>_shard2_replica_n1]
> o.a.s.h. RestoreCore Could not switch to restored index. Rolling back to the
> current index => org.apache.lucene.index.CorruptindexException: Unexpected
> file read error while reading index.
> (resource=BufferedChecksumIndexInput(segments_1g9dk))
> Caused by: java.io. FileNotFoundException: File does not exist:
> hdfs://<hdfsPath>/core_node2/data/restore/<fileName>
> It appears that Solr is looking for a file in HDFS that doesn't exist,
> despite no manual deletions being made. I cannot determine why these specific
> shards failed to restore, or why the system is unable to locate the required
> files.
> *Expected Behavior:*
> The backup and restore process should complete without errors, and all shards
> should be restored successfully to the new cluster.
> *Actual Behavior:*
> Two shards failed to restore, with errors related to missing files and index
> corruption.
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