The number of files depends on the merge factor, number of segments, and number of indexed fields in your index. It also depends on whether you are using "compound files" or not (this is a flag on the IndexWriter). With compound files flag on, segments have fixed number of files, regardless of how many fields you use. Without the flag, each field is a separate file.
Let's say you have 10 segments (per your merge factor) that are being merged into a new segment (via an optimize call or just because you have reached the merge factor). This means there are 11 segments open at the same time. If you have 20 indexed fields and are not using compound files, that's 20 * 11 = 220 files. There are a few other files open as well, plus whatever other files and sockets that your JVM process is holding open at that time. This would include incoming connections, for example, if this is running inside a web server. If you are running in an application server, this could include connections and files open by other applications in that same app server.
So the numbers run up quite a bit.
By the way, it is usual to have the file descriptors limit set at 9000 or so for unix machines running production web applications. By the way 2, on Solaris, you will need to modify a value in /etc/systems to get up to this level. Not sure about Linux or other flavors.
Another suggestion - you may want to look into a tool called "lsof". It is a utility that will show file handles open by a particular process. It could be that some other part of your process (or of the application server, VM, etc) is not closing files. This tool will help you see what files are open and you can validate that all of the really need to be open.
Best of luck. Dmitry.
Neelam Bhatnagar wrote:
Hi,
I had requested help on an issue we have been facing with the "Too many
open files" Exception garbling the search indexes and crashing the
search on the web site. As a suggestion, you had asked us to look at the articles on O'Reilly
Network which had specific context around this exact problem. One of the suggestions was to increase the limit on the number of file
descriptors on the file system. We tried it by first lowering the limit
to 200 from 256 in order to reproduce the exception. The exception did
get reproduced but even after increasing the limit to 500, the exception
kept coming until after several rounds of trying to rebuild the index,
we finally got to get it working for the default file descriptor limit
of 256. This makes us wonder if your first suggestion of optimizing
indexes is a pre-requisite to trying this option.
Another piece of relevant information is that we have the default merge factor of 10.
Kindly give us pointers to what it that we are doing wrong or should we be trying something completely different.
Thanks and regards Neelam Bhatnagar
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