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From "Erick Erickson" <erickerick...@gmail.com>
Subject Re: Combining results of multiple indexes
Date Thu, 18 Dec 2008 18:41:58 GMT
I would recommend, very strongly, that you don't rely on the doc IDs being
the same in two different indexes. Doc IDs are just incremented by one
for each doc added, but.....

optimization can change the doc ID. and is guaranteed to change at
least some of them if there are deletions from your index. If you, for
whatever reason indexed document N in one index and then skipped
it in the other, all subsequent document IDs would not match. If.....

The fact that your IDs are the same is more than undocumented, it
is coincidental.

Best
Erick

On Thu, Dec 18, 2008 at 11:46 AM, Preetham Kajekar <preetham@cisco.com>wrote:

> Hi,
> I noticed that the doc id is the same. So, if I have HitCollector, just
> collect the doc-ids of both Searchers (for the two indexes) and find the
> intersection between them, it would work. Also, get the doc is even where
> there are large number of hits is fast.
>
> Of course, I am using something undocumented of Lucene.
>
>
> Thanks,
> ~preetham
>
> Preetham Kajekar wrote:
>
>> Thanks. Yep the code is very easy. However, it take about 3 mins to
>> complete merging.
>>
>> Looks like I will need to have an out of band merging of indexes once they
>> are closed (planning to store about 50mil entries in each index partition)
>>
>>
>> However, as the data is being indexed, is there any other way to combine
>> results ?
>>
>> I could get the results of one index, get all the hits and then apply this
>> as a filter for the next index. But if there are large number of hits (which
>> is likely to be the case), this would not perform too well.
>>
>> Do you think the document id can be used in anyway. How is the document id
>> generated ? After all, i have the two indexes operating on a common List of
>> objects. Would the doc is in index1 and index2 for object N in the list be
>> the same ?
>>
>>
>> Thanks,
>> ~preetham
>>
>> Erick Erickson wrote:
>>
>>> You will be stunned at how easy it is. The merging code should be
>>> a dozen lines (and that only if you are merging 6 or so indexes)....
>>>
>>> See IndexWriter.addIndexes or
>>> IndexWriter.addIndexesNoOptimize
>>>
>>> Best
>>> Erick
>>>
>>> On Thu, Dec 18, 2008 at 5:03 AM, Preetham Kajekar <preetham@cisco.com
>>> >wrote:
>>>
>>>
>>>
>>>> Hi,
>>>> I tried out a single IndexWriter used by two threads to index different
>>>> fields. It is slower than using two separate IndexWriters. These are my
>>>> findings
>>>>
>>>> All Fields (9) using 1 IndexWriter 1 Thread - 38,000 object per sec
>>>> 5 Fields       using 1 IndexWriter 1 Thread - 62,000 object per sec
>>>> All Fields (9) using 1 IndexWriter 2 Thread - 29,000 object per sec
>>>> All Fields (9) using 2 IndexWriter 2 Thread - 55,000 object per sec
>>>>
>>>> So, it looks like I will have figure how to combine results of multiple
>>>> indexes.
>>>>
>>>> Thanks,
>>>> ~preetham
>>>>
>>>>
>>>> Preetham Kajekar wrote:
>>>>
>>>>
>>>>
>>>>> Thanks Erick and Michael.
>>>>> I will try out these suggestions and post my findings.
>>>>>
>>>>> ~preetham
>>>>>
>>>>> Erick Erickson wrote:
>>>>>
>>>>>
>>>>>
>>>>>> Well, maybe if I'd read the original post more carefully I'd have
>>>>>> figured
>>>>>> that out,
>>>>>> sorry 'bout that.
>>>>>>
>>>>>> I *think* I remember reading somewhere on the email lists that your
>>>>>> indexing
>>>>>> speed goes up pretty linearly as the number of indexing tasks
>>>>>> approaches
>>>>>> the number of CPUs. Are you, perhaps, on a dual-core machine? But
do
>>>>>> search
>>>>>> the mail archives because my memory may not be accurate.
>>>>>>
>>>>>> You can easily combine indexes by IndexWriter.addIndexes BTW.
>>>>>> Personally
>>>>>> I prefer fewer indexes if you can get away with it. But I'd only
try
>>>>>> this
>>>>>> after
>>>>>> Michael's suggestion of using multiple threads on a single underlying
>>>>>> writer.
>>>>>>
>>>>>> You could even think about using N machines to create M fragments
then
>>>>>> combining them all afterwards if your logs are static enough to make
>>>>>> that
>>>>>> reasonable. Combining indexes may take a while though.....
>>>>>>
>>>>>> Best
>>>>>> Erick
>>>>>>
>>>>>> On Wed, Dec 17, 2008 at 10:46 AM, Preetham Kajekar <
>>>>>> preetham@cisco.com
>>>>>>
>>>>>>
>>>>>>> wrote:
>>>>>>>
>>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>> Hi Erick,
>>>>>>> Thanks for the response. Replies inline.
>>>>>>>
>>>>>>> Erick Erickson wrote:
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>> The very first question is always "are you opening a new
searcher
>>>>>>>> each time you query"? But you've looked at the Wiki so I
assume not.
>>>>>>>> This question is closely tied to what kind of latency you
can
>>>>>>>> tolerate.
>>>>>>>>
>>>>>>>> A few more details, please. What's slow? Queries? Indexing?
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>> Indexing. Again, it is not slow. It is just faster with two separate
>>>>>>> indexers in two threads.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>> How slow? 100ms? 100s? What are your target times and
>>>>>>>> what are you seeing?
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>> With a single indexer in a single thread, I can index about 20,000
>>>>>>> event
>>>>>>> objects per second. With 2 thread and 2 indexers, it is close
to
>>>>>>> 50,000.
>>>>>>> :-)
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>> How big is your index? 100M? 100G? What kind of VM
>>>>>>>> parameters are you specifying?
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>> The index will have about 20mil entries. The size of the index
lands
>>>>>>> up
>>>>>>> being about 500M.
>>>>>>> I start the VM with 1G of heap. No other options for GC etc is
used.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>> As an aside, do note that there's no requirement in Lucene
that
>>>>>>>> each document have the same fields, so it's unclear why you
>>>>>>>> need two indexes, but perhaps some of the answers to the
above
>>>>>>>> will help us understand.
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>> Like I mentioned, Lucene does the job much faster with two indexes.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>> Also, be very very careful what you measure when you measure
>>>>>>>> queries. You absolutely *have* to put some instrumentation
in
>>>>>>>> the code since "slow queries" can result from things other
than
>>>>>>>> searching. For instance, iterating over a Hits object for
100s of
>>>>>>>> documents....
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>> The Query speeds are much faster than what I need :-) So no complains
>>>>>>> here.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>> Show the code, man <G>!
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>> Code below. EvIndexer is the base class. There are two subclasses
>>>>>>> which
>>>>>>> implement addEvFieldsToIndexDoc() (template pattern) to add different
>>>>>>> fields
>>>>>>> to the index. that code is also pasted below
>>>>>>>
>>>>>>> --Code ---
>>>>>>>
>>>>>>> BaseClass
>>>>>>>
>>>>>>>  public EvIndexer(String indexName) throws Exception {
>>>>>>>     this.name = indexName;
>>>>>>>     a = new KeywordAnalyzer();
>>>>>>>     INDEX_PATH = System.getProperty(StoreManager.PROP_DB_DB_LOC,
>>>>>>> "./index/");
>>>>>>>     FSDirectory directory = FSDirectory.getDirectory(INDEX_PATH
+
>>>>>>> File.separatorChar + indexName, NoLockFactory.getNoLockFactory());
>>>>>>>     indexWriter = new IndexWriter(directory, a,
>>>>>>> IndexWriter.MaxFieldLength.LIMITED);
>>>>>>> //indexWriter.setUseCompoundFile(false);
>>>>>>>     //indexWriter.setRAMBufferSizeMB(256);
>>>>>>>       }
>>>>>>>     /** Method implemented by extending classes to add data into
the
>>>>>>> index document for the
>>>>>>>  *  given event
>>>>>>>  *
>>>>>>>  * @param d
>>>>>>>  */
>>>>>>>  protected abstract void addEvFieldsToIndexDoc(Document d, Ev
event);
>>>>>>>   public void addToIndex(Ev ev) throws Exception {
>>>>>>>     noOfEventsIndexed++;
>>>>>>>     Document d = new Document();             addEvFieldsToIndexDoc(d,
>>>>>>> ev);
>>>>>>>     indexWriter.addDocument(d);
>>>>>>>           if ((noOfEventsIndexed % COMMIT_INTERVAL) == 0) {
>>>>>>>         System.out.println(name + " indexed " +
>>>>>>> NumberFormat.getInstance().format(noOfEventsIndexed) + " Commiting
>>>>>>> them");
>>>>>>>         commit();
>>>>>>>     }                   }
>>>>>>>
>>>>>>> DerievdClass1
>>>>>>>  protected void addEvFieldsToIndexDoc(Document d, Ev ev) {
>>>>>>>     //noOfEventsIndexed++;
>>>>>>>           Field id = new Field(EV_ID, Long.toString(ev.getId()),
>>>>>>> Field.Store.YES, Field.Index.NO);
>>>>>>>     Field src = new Field(EV_SRC, Long.toString(ev.getSrcId()),
>>>>>>> Field.Store.NO, Field.Index.NOT_ANALYZED);
>>>>>>>     Field type = new Field(EV_TYPE,
>>>>>>> Integer.toString(ev.getEventTypeId()), Field.Store.NO,
>>>>>>> Field.Index.NOT_ANALYZED);
>>>>>>>     Field pri = new Field(EV_PRI, Short.toString(ev.getPriority())
,
>>>>>>> Field.Store.NO, Field.Index.NOT_ANALYZED);
>>>>>>>     Field time = new Field(EV_TIME, getHexString(ev.getRecvTime())
,
>>>>>>> Field.Store.NO, Field.Index.NOT_ANALYZED);
>>>>>>>     d.add(id);
>>>>>>>     d.add(src);
>>>>>>>     d.add(type);
>>>>>>>     d.add(pri);
>>>>>>>     d.add(time);
>>>>>>>     //noOfFieldsIndexed +=  4;
>>>>>>>                 }
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Thanks for the support.
>>>>>>> ~preetham
>>>>>>>
>>>>>>>
>>>>>>>  Best
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>> Erick
>>>>>>>>
>>>>>>>>
>>>>>>>> On Wed, Dec 17, 2008 at 9:40 AM, Preetham Kajekar <
>>>>>>>> preetham@cisco.com
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>> wrote:
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>> Hi Grant,
>>>>>>>>> Thanks four response. Replies inline.
>>>>>>>>>
>>>>>>>>> Grant Ingersoll wrote:
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>> On Dec 17, 2008, at 12:57 AM, Preetham Kajekar wrote:
>>>>>>>>>>
>>>>>>>>>>  Hi,
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>> I am new to Lucene. I am not using it as a pure
text indexer.
>>>>>>>>>>>
>>>>>>>>>>> I am trying to index a Java object which has
about 10 fields
>>>>>>>>>>> (like
>>>>>>>>>>> id,
>>>>>>>>>>> time, srcIp, dstIp) - most of them being numerical
values.
>>>>>>>>>>> In order to speed up indexing, I figured that
having two separate
>>>>>>>>>>> indexers, each of them indexing different set
of fields works
>>>>>>>>>>> great.
>>>>>>>>>>> So
>>>>>>>>>>> I
>>>>>>>>>>> have the first 5 fields in index1 and the remaining
in index2.
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>> Can you explain this a bit more?  Are those two fields
really
>>>>>>>>>> large
>>>>>>>>>> org
>>>>>>>>>> something?  How are you obtaining them?  How are
you correlating
>>>>>>>>>> the
>>>>>>>>>> documents between the two indexes?  Did you actually
try a single
>>>>>>>>>> index
>>>>>>>>>> and
>>>>>>>>>> it was too slow?
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>> I have a java object which has about 10 fields. However,
the fields
>>>>>>>>> are
>>>>>>>>> not
>>>>>>>>> fixed. The java object is essentially a representation
of Syslogs
>>>>>>>>> from
>>>>>>>>> network devices. So different syslogs have different
fields. Each
>>>>>>>>> field
>>>>>>>>> has
>>>>>>>>> a unique id and a value (mostly numeric types, so i convert
it to
>>>>>>>>> string).
>>>>>>>>> There are some fixed fields. So the object is a list
of fields
>>>>>>>>> which
>>>>>>>>> is
>>>>>>>>> produced by a parser.
>>>>>>>>> I am trying to index using two indexers in two separate
threads-
>>>>>>>>> one
>>>>>>>>> for
>>>>>>>>> fixed and another for the non-fixed fields. Except for
a unique id,
>>>>>>>>> I
>>>>>>>>> do
>>>>>>>>> not
>>>>>>>>> store the fields in Lucene - i just index them. From
the index, i
>>>>>>>>> get
>>>>>>>>> the
>>>>>>>>> unique id which is all I care about. (the objects are
stored
>>>>>>>>> elsewhere
>>>>>>>>> and
>>>>>>>>> can be looked up based on this unique id).
>>>>>>>>> I did try using a single indexer, but things were quite
slow.
>>>>>>>>> Getting
>>>>>>>>> high
>>>>>>>>> throughput is crucial and having two indexers seemed
to do very
>>>>>>>>> well.
>>>>>>>>> (more
>>>>>>>>> than twice as fast)
>>>>>>>>>
>>>>>>>>> Further, the index will never be modified and I can have
just one
>>>>>>>>> thread
>>>>>>>>> writing to the index. If there are any other performance
tips would
>>>>>>>>> be
>>>>>>>>> very
>>>>>>>>> helpful. I have already looked at the wiki link regarding
>>>>>>>>> performance
>>>>>>>>> and
>>>>>>>>> using some of them.
>>>>>>>>>
>>>>>>>>> Thanks,
>>>>>>>>> ~preetham
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>> Now, I want to have boolean AND query's looking for
values in both
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>> indexes. Like f1=1234 AND f7=ABCD.f1 and f7 and
present in two
>>>>>>>>>>> separate
>>>>>>>>>>> indexes. Would using the MultiIndexReader help
? Since I am doing
>>>>>>>>>>> an
>>>>>>>>>>> AND, I
>>>>>>>>>>> dont expect that it would work.
>>>>>>>>>>>
>>>>>>>>>>> Thanks,
>>>>>>>>>>> ~preetham
>>>>>>>>>>>
>>>>>>>>>>> ---------------------------------------------------------------------
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> To unsubscribe, e-mail: java-user-unsubscribe@lucene.apache.org
>>>>>>>>>>> For additional commands, e-mail:
>>>>>>>>>>> java-user-help@lucene.apache.org
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>> --------------------------
>>>>>>>>>> Grant Ingersoll
>>>>>>>>>>
>>>>>>>>>> Lucene Helpful Hints:
>>>>>>>>>> http://wiki.apache.org/lucene-java/BasicsOfPerformance
>>>>>>>>>> http://wiki.apache.org/lucene-java/LuceneFAQ
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> ---------------------------------------------------------------------
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> To unsubscribe, e-mail: java-user-unsubscribe@lucene.apache.org
>>>>>>>>>> For additional commands, e-mail: java-user-help@lucene.apache.org
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>> ---------------------------------------------------------------------
>>>>>>>>>
>>>>>>>>> To unsubscribe, e-mail: java-user-unsubscribe@lucene.apache.org
>>>>>>>>> For additional commands, e-mail: java-user-help@lucene.apache.org
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>> ---------------------------------------------------------------------
>>>>>>>
>>>>>>> To unsubscribe, e-mail: java-user-unsubscribe@lucene.apache.org
>>>>>>> For additional commands, e-mail: java-user-help@lucene.apache.org
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>> ---------------------------------------------------------------------
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>>>> For additional commands, e-mail: java-user-help@lucene.apache.org
>>>>
>>>>
>>>>
>>>>
>>>
>>>
>>>
>>
>>
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