plus 2 means search a term need seek many times for tis(if it's not cached in tii)
2010/12/31 Li Li <fancye...@gmail.com>: > searching multi segments is a alternative solution but it has some > disadvantages. > 1. idf is not global?(I am not familiar with its implementation) maybe > it's easy to solve it by share global idf > 2. each segments will has it's own tii and tis files, which may make > search slower(that's why optimization of > index is neccessary) > 3. one term's docList is distributed in many files rather than one. > more than one frq files means > hard disk must seek different tracks, it's time consuming. if there is > only one segment, the are likely > stored in a single track. > > > 2010/12/31 Earwin Burrfoot <ear...@gmail.com>: >>>>>until we fix Lucene to run a single search concurrently (which we >>>>>badly need to do). >>> I am interested in this idea.(I have posted it before) do you have some >>> resources such as papers or tech articles about it? >>> I have tried but it need to modify index format dramatically and we use >>> solr distributed search to relieve the problem of response time. so finally >>> give it up. >>> lucene4's index format is more flexible that it supports customed codecs >>> and it's now on development, I think it's good time to take it into >>> consideration >>> that let it support multithread searching for a single query. >>> I have a naive solution. dividing docList into many groups >>> e.g grouping docIds by it's even or odd >>> term1 df1=4 docList = 0 4 8 10 >>> term1 df2=4 docList = 1 3 9 11 >>> >>> term2 df1=4 docList = 0 6 8 12 >>> term2 df2=4 docList = 3 9 11 15 >>> then we can use 2 threads to search topN docs on even group and odd group >>> and finally merge their results into a single on just like solr >>> distributed search. >>> But it's better than solr distributed search. >>> First, it's in a single process and data communication between >>> threads is much >>> faster than network. >>> Second, each threads process the same number of documents.For solr >>> distributed >>> search, one shard may process 7 documents and another shard may 1 document >>> Even if we can make each shard have the same document number. we can not >>> make it uniformly for each term. >>> e.g. shard1 has doc1 doc2 >>> shard2 has doc3 doc4 >>> but term1 may only occur in doc1 and doc2 >>> while term2 may only occur in doc3 and doc4 >>> we may modify it >>> shard1 doc1 doc3 >>> shard2 doc2 doc4 >>> it's good for term1 and term2 >>> but term3 may occur in doc1 and doc3... >>> So I think it's fine-grained distributed in index while solr >>> distributed search is coarse- >>> grained. >> This is just crazy :) >> >> The simple way is just to search different segments in parallel. >> BalancedSegmentMergePolicy makes sure you have roughly even-sized >> large segments (and small ones don't count, they're small!). >> If you're bound on squeezing out that extra millisecond (and making >> your life miserable along the way), you can search a single segment >> with multiple threads (by dividing it in even chunks, and then doing >> skipTo to position your iterators to the beginning of each chunk). >> >> First approach is really easy to implement. Second one is harder, but >> still doesn't require you to cook the number of CPU cores available >> into your index! >> >> It's the law of diminishing returns at play here. You're most likely >> to search in parallel over mostly memory-resident index >> (RAMDir/mmap/filesys cache - doesn't matter), as most of IO subsystems >> tend to slow down considerably on parallel sequential reads, so you >> already have pretty decent speed. >> Searching different segments in parallel (with BSMP) makes you several >> times faster. >> Searching in parallel within a segment requires some weird hacks, but >> has maybe a few percent advantage over previous solution. >> Sharding posting lists requires a great deal of weird hacks, makes >> index machine-bound, and boosts speed by another couple of percent. >> Sounds worthless. >> >> -- >> Kirill Zakharenko/Кирилл Захаренко (ear...@gmail.com) >> Phone: +7 (495) 683-567-4 >> ICQ: 104465785 >> >> --------------------------------------------------------------------- >> To unsubscribe, e-mail: dev-unsubscr...@lucene.apache.org >> For additional commands, e-mail: dev-h...@lucene.apache.org >> >> > --------------------------------------------------------------------- To unsubscribe, e-mail: dev-unsubscr...@lucene.apache.org For additional commands, e-mail: dev-h...@lucene.apache.org
