[jira] [Commented] (SOLR-4909) Solr and IndexReader Re-opening on Replication Slave

["Robert Muir (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SOLR-4909?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13742908#comment-13742908 ] 

Robert Muir commented on SOLR-4909:
-----------------------------------

Hi Michael: 

So the idea here is an explicit option that allows to not reopen from indexwriter for these replication slaves (because a new IW is created when replication happens?)

This piece one concerns me:
{quote}
There is logic in SolrCore.openNewSearcher to open a new reader rather than re-open should the underlying directory instance in the current reader not match that of the new index writer as that means that a full copy of the index was downloaded into a new directory, as would happen during replication if the slave's version was ahead of the master's.
{quote}

{noformat}
+            // during a replication that pulls the complete index into a new physical directory
+            // the reader cannot be reopened and must be newly opened using the same directory as the writer
+            if(writer != null && !currentReader.directory().equals(writer.get().getDirectory())) {
{noformat}

Are you sure this really does what you want? I don't think anybody implements/tests equals() on Directory implementations, and if so I'm not sure what the semantics would be. Looking at other stuff around this code that tries to do similar things, it seems they are comparing strings (representing the directory path).
                
> Solr and IndexReader Re-opening on Replication Slave
> ----------------------------------------------------
>
>                 Key: SOLR-4909
>                 URL: https://issues.apache.org/jira/browse/SOLR-4909
>             Project: Solr
>          Issue Type: Improvement
>          Components: replication (java), search
>    Affects Versions: 4.3
>            Reporter: Michael Garski
>             Fix For: 4.5, 5.0
>
>         Attachments: SOLR-4909-demo.patch, SOLR-4909_fix.patch, SOLR-4909_v2.patch
>
>
> I've been experimenting with caching filter data per segment in Solr using a CachingWrapperFilter & FilteredQuery within a custom query parser (as suggested by [~yonik@apache.org] in SOLR-3763) and encountered situations where the value of getCoreCacheKey() on the AtomicReader for each segment can change for a given segment on disk when the searcher is reopened. As CachingWrapperFilter uses the value of the segment's getCoreCacheKey() as the key in the cache, there are situations where the data cached on that segment is not reused when the segment on disk is still part of the index. This affects the Lucene field cache and field value caches as well as they are cached per segment.
> When Solr first starts it opens the searcher's underlying DirectoryReader in StandardIndexReaderFactory.newReader by calling DirectoryReader.open(indexDir, termInfosIndexDivisor), and the reader is subsequently reopened in SolrCore.openNewSearcher by calling DirectoryReader.openIfChanged(currentReader, writer.get(), true). The act of reopening the reader with the writer when it was first opened without a writer results in the value of getCoreCacheKey() changing on each of the segments even though some of the segments have not changed. Depending on the role of the Solr server, this has different effects:
> * On a SolrCloud node or free-standing index and search server the segment cache is invalidated during the first DirectoryReader reopen - subsequent reopens use the same IndexWriter instance and as such the value of getCoreCacheKey() on each segment does not change so the cache is retained. 
> * For a master-slave replication set up the segment cache invalidation occurs on the slave during every replication as the index is reopened using a new IndexWriter instance which results in the value of getCoreCacheKey() changing on each segment when the DirectoryReader is reopened using a different IndexWriter instance.
> I can think of a few approaches to alter the re-opening behavior to allow reuse of segment level caches in both cases, and I'd like to get some input on other ideas before digging in:
> * To change the cloud node/standalone first commit issue it might be possible to create the UpdateHandler and IndexWriter before the DirectoryReader, and use the writer to open the reader. There is a comment in the SolrCore constructor by [~yonik@apache.org] that the searcher should be opened before the update handler so that may not be an acceptable approach. 
> * To change the behavior of a slave in a replication set up, one solution would be to not open a writer from the SnapPuller when the new index is retrieved if the core is enabled as a slave only. The writer is needed on a server configured as a master & slave that is functioning as a replication repeater so downstream slaves can see the changes in the index and retrieve them.
> I'll attach a unit test that demonstrates the behavior of reopening the DirectoryReader and it's effects on the value of getCoreCacheKey. My assumption is that the behavior of Lucene during the various reader reopen operations is correct and that the changes are necessary on the Solr side of things.

--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators
For more information on JIRA, see: http://www.atlassian.com/software/jira

---------------------------------------------------------------------
To unsubscribe, e-mail: dev-unsubscribe@lucene.apache.org
For additional commands, e-mail: dev-help@lucene.apache.org