That's funny you bring that up- because I was JUST discussing this as a possibility with a coworker. Compaction is really the phase that I'm concerned with- as the API for loading the data from the TopN currently only allows you to load the last N keys/values for a single index at a time.
Can I guarantee that compaction will pass each row through a single filter? On Jan 3, 2013, at 5:54 PM, Keith Turner wrote: > Data is read from the iterators into a buffer. When the buffer fills > up, the data is sent to the client and the iterators are reinitialized > to fill up the next buffer. > > The default buffer size was changed from 50M to 1M at some point. > This is configured via the property table.scan.max.memory > > The lower buffer size will cause iterator to be reinitialized more > frequently. Maybe you are seeing this. > > Keith > > On Thu, Jan 3, 2013 at 5:41 PM, Corey Nolet <[email protected]> wrote: >> Hey Guys, >> >> In "Accumulo 1.3.5", I wrote a "Top N" table structure, services and a >> FilteringIterator that would allow us to drop in several keys/values >> associated with a UUID (similar to a document id). The UUID was further >> associated with an "index" (or type). The purpose of the TopN table was to >> keep the keys/values separated so that they could still be queried back with >> cell-level tagging, but when I performed a query for an index, I would get >> the last N UUIDs and further be able to query the keys/values for each of >> those UUIDs. >> >> This problem seemed simple to solve in Accumulo 1.3.5, as I was able to >> provide 2 FilteringIterators for compaction time to perform data cleanup of >> the table so that any keys/values kept around were guaranteed to be inside >> of the range of those keys being managed by the versioning iterator. >> >> Just to recap, I have the following table structure. I also hash the >> keys/values and run a filter before the versioning iterator to clean up any >> duplicates. There are two types of columns: index & key/value. >> >> >> Index: >> >> R: index (or "type" of data) >> F: '\x00index' >> Q: empty >> V: uuid\x00hashOfKeys&Values >> >> >> Key/Value: >> >> R: index (or "type" of data) >> F: uuid >> Q: key\x00value >> V: empty >> >> >> The filtering iterator that makes sure any key/value rows are in the index >> manages a hashset internally. The index rows are purposefully indexed before >> the key/value rows so that the filter can build up the hashset containing >> those uuids in the index. As the filter iterates into the key/value rows, it >> will return true only if the uuid of the key/value exists inside of the >> hashset containing the uuids in the index. This worked with older versions >> of accumulo but I'm now getting a weird artifact where INIT() is called on >> my Filter in the middle of iterating through an index row. >> >> More specifically, the Filter will iterate through the index rows of a >> specific "index" and build up a hashset, then init() will be called which >> wipes away the hashset of uuids, then the further goes on to iterate through >> the key/value rows. Keep in mind, we are talking about maybe 400k entries, >> not enough to have more than 1 tablet. >> >> Any idea why this may have worked on 1.3.5 but doesn't work any longer? I >> know it has got to be a huge nono to be storing state inside of a filter, >> but I haven't had any issues until trying to update my code for the new >> version. If I'm doing this completely wrong, any ideas on how to make this >> better? >> >> >> Thanks! >> >> >> -- >> Corey Nolet >> Senior Software Engineer >> TexelTek, inc. >> [Office] 301.880.7123 >> [Cell] 410-903-2110
