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From John Vines <>
Subject Re: Filter storing state
Date Thu, 03 Jan 2013 22:53:29 GMT
Are you testing this in scan time or via actual minor/major compactions? I
know at scan time, there is no guarantee that the iterator remains intact
through the entire scan, and it instead may be reconstructed, causing state
to be lost. I don't think this is the case for compaction time iterators,
but I'm not positive.

On Thu, Jan 3, 2013 at 5:41 PM, Corey Nolet <> 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

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