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https://issues.apache.org/jira/browse/SOLR-9091?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15277172#comment-15277172
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Uwe Schindler commented on SOLR-9091:
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bq. Is it possible that the segment identifiers generated in core B may have an
overlap with those in core A ?
Unlikely, but theoretically possible - this can be compared to the possibility
of 2 different files could have the same SHA1 hash. If it ever happens, we have
to revisit the random number generator behind it.
Just to note: The identifiers are excatly there to prevent the problem you are
describing. So please use them for that, no need to revisit this again. You can
be 99.99999999999...% sure that 2 segment files with identical filename,
identical identifier and identical hash are the same files.
> Solr index restore silently copies the corrupt segments in the backup
> ---------------------------------------------------------------------
>
> Key: SOLR-9091
> URL: https://issues.apache.org/jira/browse/SOLR-9091
> Project: Solr
> Issue Type: Bug
> Reporter: Hrishikesh Gadre
>
> The Solr core restore functionality uses following criteria to decide if a
> given file is copied from backup directory or from current index directory.
> case 1] File is available in both backup and current index directory
> --> Compare the checksum and file length
> --> If checksum and length matching, copy the file from current working
> directory.
> --> If the checksum and length doesn't match, copy the file from backup
> directory.
> case 2] File is available in only in backup directory (This can happen for a
> newly created core without any data).
> --> Copy the file from backup directory.
> Now the problem here is that we intentionally catch and ignore the error
> while reading the checksum for a file in the backup directory. Hence in case
> (2), it will result into restoration of a file without appropriate "checksum".
> Here is the relevant code snippet,
> https://github.com/apache/lucene-solr/blob/a5586d29b23f7d032e6d8f0cf8758e56b09e0208/solr/core/src/java/org/apache/solr/handler/RestoreCore.java#L82-L95
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