[LUCENE-8149] NRTCachingDirectory does not need to preemptively delete segment files and generate exceptions

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 7.3
• Lucene Fields: New
• Assignee: Erick Erickson
• Reporter: Erick Erickson
• Created: 01/Feb/18 06:02
• Updated: 28/Aug/22 15:25
• Resolved: 05/Feb/18 19:26

Description

Moving over here from SOLR-11892. After getting through my confusion I've found the following: NRTCachingDirectory.createOutput tries to delete segment files before creating them. We should at least add a bit of commentary as to what the pre-emptive delete is there for since on the surface it's not obvious.

try {
in.deleteFile(name);
{{ } catch (IOException ioe) {}}
// This is fine: file may not exist
{{ }}}

If I change to using MMapDirectory or NIOFSDirectory these exceptions are not thrown. What's special about NRTCachingDirectory that it needs this when two of the possible underlying FS implementations apparently do not? Or is this necessary for, say, Windows or file systems than the two I tried? Or is it some interaction between the RAM based segments and segments on disk?

Issue Links

• relates to: SOLR-11892 Avoid unnecessary exceptions in FSDirectory and RAMDirectory