> From: Mark Tucker [mailto:[EMAIL PROTECTED]]
>
> What is the best way to
> move the index from the build server to the search servers
> and then change which index a user is searching against? I
> am concerned about switching the index while a user is paging
> through search results. Ideally new users will access the
> new index while current users will access the old index. How
> will I know when all current users are no longer accessing
> the old index so that it can be deleted?
If you're using Unix, this is easy. Once an IndexReader is created, it
keeps open all files it needs. Since Unix lets you delete files that are
open, there's no conflict. When the last search using the old IndexReader
completes and it is garbage collected, finalizers will close the files and
the OS will free the disk space.
The simplest approach on Unix is probably to use a symbolic link to the
latest version of the index. When a new index is installed, just update the
symbolic link to the new index and delete the old one: "ln -sf new latest;
rm -rf old".
Use something like the following to cache the reader for the index in
"latest":
private IndexReader reader;
private long readerLastModified;
public synchronized IndexReader getIndexReader() {
if (lastModified != IndexReader.lastModified("latest")) {
// there's a new index: open it
lastModified = IndexReader.lastModified("latest");
indexReader = IndexReader.open("latest");
}
return indexReader;
}
If you call this for each search, then searches will always search the
latest index. It's most efficient keep just one IndexReader per index for
searching.
On Win32 there are two complications. First, you cannot use a symbolic link
to refer to the latest version of the index. Nor can you rename or
overwrite the existing index, since it has open files. So you must do
something like list a directory, looking for a new index directory. Second,
you need to wait until all searches are complete before the old index can be
deleted. You can either spawn a thread that keeps trying to delete it.
When the last search exits and the IndexWriter is garbage collected this
will succeed. A riskier approach is simply to wait five minutes, then call
IndexReader.close(), then delete it. Any searches in progress on the old
index will crash when it is closed, but the delete should succeed! If
anyone knows a way around these Win32 issues, I'd love to hear it.
Doug
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