[ http://issues.apache.org/jira/browse/LUCENE-687?page=comments#action_12445979 ] Yonik Seeley commented on LUCENE-687: -------------------------------------
I tried with the boolean, but it made no difference with 1.5 or 1.6 server JVMs. The overhead is probably due to increased state in the object as well as an unpredictable branch in the inner loop. I'm not too worried though... my artificial test isn't really representative if the common usecases of phrase queries on full-text fields which have more varied term frequencies and more positions per document. > Performance improvement: Lazy skipping on proximity file > -------------------------------------------------------- > > Key: LUCENE-687 > URL: http://issues.apache.org/jira/browse/LUCENE-687 > Project: Lucene - Java > Issue Type: Improvement > Components: Index > Reporter: Michael Busch > Assigned To: Yonik Seeley > Priority: Minor > Fix For: 2.1 > > Attachments: lazy_prox_skipping.patch, lazy_prox_skipping2.patch > > > Hello, > I'm proposing a patch here that changes > org.apache.lucene.index.SegmentTermPositions to avoid unnecessary skips and > reads on the proximity stream. Currently a call of next() or seek(), which > causes a movement to a document in the freq file also moves the prox pointer > to the posting list of that document. But this is only necessary if actual > positions have to be retrieved for that particular document. > Consider for example a phrase query with two terms: the freq pointer for term > 1 has to move to document x to answer the question if the term occurs in that > document. But *only* if term 2 also matches document x, the positions have to > be read to figure out if term 1 and term 2 appear next to each other in > document x and thus satisfy the query. > A move to the posting list of a document can be quite expensive. It has to be > skipped to the last skip point before that document and then the documents > between the skip point and the desired document have to be scanned, which > means that the VInts of all positions of those documents have to be read and > decoded. > An improvement is to move the prox pointer lazily to a document only if > nextPosition() is called. This will become even more important in the future > when the size of the proximity file increases (e. g. by adding payloads to > the posting lists). > My patch implements this lazy skipping. All unit tests pass. > I also attach a new unit test that works as follows: > Using a RamDirectory an index is created and test docs are added. Then the > index is optimized to make sure it only has a single segment. This is > important, because IndexReader.open() returns an instance of SegmentReader if > there is only one segment in the index. The proxStream instance of > SegmentReader is package protected, so it is possible to set proxStream to a > different object. I am using a class called SeeksCountingStream that extends > IndexInput in a way that it is able to count the number of invocations of > seek(). > Then the testcase searches the index using a PhraseQuery "term1 term2". It is > known how many documents match that query and the testcase can verify that > seek() on the proxStream is not called more often than number of search hits. > Example: > Number of docs in the index: 500 > Number of docs that match the query "term1 term2": 5 > Invocations of seek on prox stream (old code): 29 > Invocations of seek on prox stream (patched version): 5 > - Michael -- This message is automatically generated by JIRA. - If you think it was sent incorrectly contact one of the administrators: http://issues.apache.org/jira/secure/Administrators.jspa - For more information on JIRA, see: http://www.atlassian.com/software/jira --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
