Re: Real time indexing and distribution to lucene on separate boxes (long)
--- Kevin A. Burton [EMAIL PROTECTED] wrote: Otis Gospodnetic wrote: I like option 3. I've done it before, and it worked well. I dealt with very small indices, though, and if your indices are several tens or hundred gigs, this may be hard for you. Option 4: search can be performed on an index that is being modified (update, delete, insert, optimize). You'd just have to make sure not to recreate new IndexSearcher too frequently, if your index is being modified often. Just change it every X index modification or every X minutes, and you'll be fine. Right now I'm thinking about #4... Disk may be cheap but a fast RAID 10 array with 100G twice isn't THAT cheap... That's the worse case Yes, but not everything needs to be on a fast RAID (you probabably are using SCSI disks in RAID, which is what makes it expensive. RAID requires only a RAID controller). You could have a Searcher machine with a set of cheap EIDE disks, and use those as a copy target disks, which are not searched. Once you transfer your indices there, you copy them on fast SCSI RAID disks. Also... since the new indexes are SO small (~100M) the merges would probably be easier on the machine than just doing a whole new write. Of course it's hard to make that argument with a 100G RAID array but we're using rysnc to avoid distribution of network IO so the CPU computation and network read would slow things down. The only way around this is the re-upload the whole 100G index but even over gigabit ethernet this will take 15 minutes. This doesn't scale as we add more searchers. I wonder what happens if you try compressing the indices before copying them over the network. I wonder if it makes a difference whether you use compound vs. traditional directories. I wonder what the index size is if you use DbDirectory instead of FSDirectory. Otis - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Real time indexing and distribution to lucene on separate boxes (long)
I'm curious to find out what others are doing in this situation. I have two boxes... the indexer and the searcher. The indexer is taking documents and indexing them and creating indexes in a RAMDirectory (for efficiency) and is then writing these indexes to disk as we begin to run out of memory. Usually these aren't very big... 15-100M or so. Obviously I'm dividing the indexing and searching onto dedicated boxes to improve efficiency. The real issue though is that the searchers need to be live all the time as indexes are being added at runtime. So if that wasn't clear. I actually have to push out fresh indexes WHILE users are searching them. Not a very easy thing to do. Here's my question. What are the optimum ways to then distribute these index segments to the secondary searcher boxes. I don't want to use the MultiSearcher because it's slow once we have too many indexes (see my PS) Here's what I'm currently thinking: 1. Have the indexes sync'd to the searcher as shards directly. This doesn't scale as I would have to use the MultiSearcher which is slow when it has too many indexes. (And ideally we would want an optimized index). 2. Merge everything into one index on the indexer. Lock the searcher, then copy over the new index via rsync. The problem here is that the searcher would need to lock up while the sync is happening to prevent reads on the index. If I do this enough and the system is optimzed I think I would only have to block for 5 seconds or so but that's STILL very long. 3. Have two directories on the searcher. The indexer would then sync to a tmp directory and then at run time swap them via a rename once the sync is over. The downside here is that this will take up 2x disk space on the searcher. The upside is that the box will only slow down while the rsync is happening. 4. Do a LIVE index merge on the production box. This might be an interesting approach. The major question I have is whether you can do an optimize/merge on an index that's currently being used. I *think* it might be possible but I'm not sure. This isn't as fast as performing the merge on the indexer before hand but it does have the benefits of both worlds. If anyone has any other ideas I would be all ears... PS.. Random question. The performance of the MultiSearcher is Mlog(N) correct? Where N is the number of documents in the index and M is the number of indexes? Is this about right? -- Please reply using PGP. http://peerfear.org/pubkey.asc NewsMonster - http://www.newsmonster.org/ Kevin A. Burton, Location - San Francisco, CA, Cell - 415.595.9965 AIM/YIM - sfburtonator, Web - http://peerfear.org/ GPG fingerprint: 5FB2 F3E2 760E 70A8 6174 D393 E84D 8D04 99F1 4412 IRC - freenode.net #infoanarchy | #p2p-hackers | #newsmonster signature.asc Description: OpenPGP digital signature
Re: Real time indexing and distribution to lucene on separate boxes (long)
Kevin A. Burton wrote: 3. Have two directories on the searcher. The indexer would then sync to a tmp directory and then at run time swap them via a rename once the sync is over. The downside here is that this will take up 2x disk space on the searcher. The upside is that the box will only slow down while the rsync is happening. For maximal search performance, this is your best bet. Disk space is cheap. At some point all newly issued queries start going against the new index, and, pretty soon, you can close and delete the old index. But you never have to stop searching. Disk i/o will spike a bit during the changeover, as the new working set is swapped in. Note that, if folks are paging through results by re-querying (the standard method) and the index is updated then things can get funky. One approach is to hang onto the old index longer, to make this less likely. In any case, you might want to add an index-id to the search parameters, so that, if a next-page is issued when the index is no longer there you can give some sort of stale query error. PS.. Random question. The performance of the MultiSearcher is Mlog(N) correct? Where N is the number of documents in the index and M is the number of indexes? Is this about right? No. The added cost of a MultiSearcher is mostly proportional to just M, the number of indexes. The normal cost of searching is still mostly proportional to N, the number of documents. So M+N would probably be more accurate. There is a log(M) here and there, to, e.g., figure out which index a doc id belongs to, but I doubt these are significant. The significant costs of a MultiSearcher over an IndexSearcher are that it adds more term dictionary reads (one per query term per index) and more seeks (also one per query term per index, or two if you're using phrases). Doug - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: Real time indexing and distribution to lucene on separate boxes (long)
Otis Gospodnetic wrote: I like option 3. I've done it before, and it worked well. I dealt with very small indices, though, and if your indices are several tens or hundred gigs, this may be hard for you. Option 4: search can be performed on an index that is being modified (update, delete, insert, optimize). You'd just have to make sure not to recreate new IndexSearcher too frequently, if your index is being modified often. Just change it every X index modification or every X minutes, and you'll be fine. Right now I'm thinking about #4... Disk may be cheap but a fast RAID 10 array with 100G twice isn't THAT cheap... That's the worse case scenario of course and most modern search clusters use cheap hardware though... Also... since the new indexes are SO small (~100M) the merges would probably be easier on the machine than just doing a whole new write. Of course it's hard to make that argument with a 100G RAID array but we're using rysnc to avoid distribution of network IO so the CPU computation and network read would slow things down. The only way around this is the re-upload the whole 100G index but even over gigabit ethernet this will take 15 minutes. This doesn't scale as we add more searchers. Thanks for the feedback! I think now tha tI know that optmize is safe as long as I don't create a new reader... I'll be fine. I do have think about how I'm going to handle search result nav. Kevin -- Please reply using PGP. http://peerfear.org/pubkey.asc NewsMonster - http://www.newsmonster.org/ Kevin A. Burton, Location - San Francisco, CA, Cell - 415.595.9965 AIM/YIM - sfburtonator, Web - http://peerfear.org/ GPG fingerprint: 5FB2 F3E2 760E 70A8 6174 D393 E84D 8D04 99F1 4412 IRC - freenode.net #infoanarchy | #p2p-hackers | #newsmonster signature.asc Description: OpenPGP digital signature
Re: Real time indexing and distribution to lucene on separate boxes (long)
To clarify how option 3 works: You have dira where the search is done and dirb where the indexing is done. dirb grows when you add new items to it, and at some point you swap and dirb becomes dira, but what do you do then? Also, how do you write from the indexer to the directory on the search box? We had two different ideas on how to do this, we ended up implementing option 2, but you need to have support for snapshots to be able to do it. 1. Similar idea to what you were suggesting, but optimizing the index: 1. The searcher reads from dira. 2. The writer writes to dirb which contains only *new* documents that aren't in dira. 3. Periodically the writer stops writing and merges/optimizes dira and dirb to dirc. 4. When done, the writer removes dirb and starts writing to it new documents. 5. The searcher notices that dirc is ready. Renames dira to something else, renames dirc to dira. The main problem with this approach is that the merging/optimizing can be slow on large indexes. Even on fast machines with fast disks merging several Gigs takes a while. 2. The index is NFS mounted. The indexer keeps writing to the index, and at defined times, creates a NFS snapshot of the index. It then creates an entry in a db to let the searcher know that a new snapshot has been created. The searcher checks once a minute the db to see if there's a new snapshot. If there is one, it opens the index in the new snapshot and swaps it for the old one. The code to do this is synchronized. The nice thing about this solution is that you don't have just one copy of the index and don't do any copying. But you need to use NFS and snapshots. Dror On Thu, Mar 11, 2004 at 09:21:07AM -0800, Doug Cutting wrote: Kevin A. Burton wrote: 3. Have two directories on the searcher. The indexer would then sync to a tmp directory and then at run time swap them via a rename once the sync is over. The downside here is that this will take up 2x disk space on the searcher. The upside is that the box will only slow down while the rsync is happening. For maximal search performance, this is your best bet. Disk space is cheap. At some point all newly issued queries start going against the new index, and, pretty soon, you can close and delete the old index. But you never have to stop searching. Disk i/o will spike a bit during the changeover, as the new working set is swapped in. Note that, if folks are paging through results by re-querying (the standard method) and the index is updated then things can get funky. One approach is to hang onto the old index longer, to make this less likely. In any case, you might want to add an index-id to the search parameters, so that, if a next-page is issued when the index is no longer there you can give some sort of stale query error. PS.. Random question. The performance of the MultiSearcher is Mlog(N) correct? Where N is the number of documents in the index and M is the number of indexes? Is this about right? No. The added cost of a MultiSearcher is mostly proportional to just M, the number of indexes. The normal cost of searching is still mostly proportional to N, the number of documents. So M+N would probably be more accurate. There is a log(M) here and there, to, e.g., figure out which index a doc id belongs to, but I doubt these are significant. The significant costs of a MultiSearcher over an IndexSearcher are that it adds more term dictionary reads (one per query term per index) and more seeks (also one per query term per index, or two if you're using phrases). Doug - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] -- Dror Matalon Zapatec Inc 1700 MLK Way Berkeley, CA 94709 http://www.fastbuzz.com http://www.zapatec.com - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
