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From "Shai Erera (JIRA)" <j...@apache.org>
Subject [jira] Created: (LUCENE-2592) Add static readSnapshotsInfo to PersistentSnapshotDeletionPolicy
Date Tue, 10 Aug 2010 10:34:15 GMT
Add static readSnapshotsInfo to PersistentSnapshotDeletionPolicy
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                 Key: LUCENE-2592
                 URL: https://issues.apache.org/jira/browse/LUCENE-2592
             Project: Lucene - Java
          Issue Type: Improvement
          Components: Index
            Reporter: Shai Erera
            Assignee: Shai Erera
            Priority: Minor
             Fix For: 3.1, 4.0


PSDP persists the snapshots information in a Directory. When you open PSDP, it obtains a write
lock on the snapshots dir (by keeping an open IndexWriter), and updates the directory when
snapshots are created/released.

This causes problem in the following scenario -- you have two processes, one updates the 'content'
index and keeps PSDP open (because it also takes snapshots). Another process wants to read
the existing snapshots information and open a read-only IndexReader on the 'content' index.
The other process cannot read the existing snapshots information, because p1 keeps a write
lock on the snapshots directory.

There are two possible solutions:
# Have PSDP open the IndexWriter over the directory for each snapshot/release. A bit expensive,
and unnecessary.
# Introduce a static readSnapshotsInfo on PSDP which accepts a Directory and returns the snapshots
information. IMO it's cleaner, and won't have the performance overhead of opening/closing
the IW as before.

I'll post a patch (implementing the 2nd approach) shortly. I'd appreciate any comments.

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