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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