Doron Cohen wrote:
Antony Bowesman <[EMAIL PROTECTED]> wrote on 28/05/2007 22:48:41:
I read the new IndexWriter Javadoc and I'm unclear about this
autocommit. In
2.1, I thought an IndexReader opened in an IndexSearcher does not "see"
additions to an index made by an IndexWriter, i.e. maxDoc and
numDocs remain
constant, so the statement
"When autoCommit is true then every flush is also a commit (IndexReader
instances will see each flush as changes to the index). This is
the default, to
match the behavior before 2.2"
makes me wonder if my assumptions are wrong. Can you clarify
what it means by
the IndexReader "seeing" changes to the index?
Antony, your assumptions were (and still are) correct - once
an index reader is opened it is unaffected by changes to the
underlying index. Would it be clearer if the javadoc said:
"(An IndexReader instance will see changes to the index caused
by flush operations that completed prior to opening that
IndexReader instance)."?
Thanks Doron, I understood "IndexReader instance" as one that was already open,
as it's not possible to 'open' an existing object instance, the static open()
methods create new instances.
Your explanation clarifies things. So, the scenario where the IndexReader sees
changes with autocommit=true is
BEGIN
IndexWriter - open
- add documents
- some merges/flushes occur here
IndexReader - open
- sees index with results of earlier merges
IndexWriter - close
END
whereas with autocommit=false, the IndexReader would see the state of the index
at BEGIN and any merges/flushes would not show.
Perhaps the text could then be something like
"(Changes to the index caused by flush operations will be visible to an
IndexReader when it is opened prior to closing the IndexWriter)"
It would also be worth updating the isCurrent() Javadoc to clarify its
behaviour. Presumably, with autocommit=false, isCurrent() will always return
true is only using the IndexWriter to add/delete documents.
Antony
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