Home | About | Sematext search-lucene.com search-hadoop.com
 Search Hadoop and all its subprojects:

Switch to Plain View
Accumulo, mail # user - Filter storing state


+
Corey Nolet 2013-01-03, 22:41
+
Keith Turner 2013-01-03, 22:54
+
Corey Nolet 2013-01-03, 23:08
+
Keith Turner 2013-01-03, 23:10
+
Corey Nolet 2013-01-03, 23:48
+
John Vines 2013-01-03, 22:53
Copy link to this message
-
Re: Filter storing state
Corey Nolet 2013-01-03, 23:04
John thanks for the quick response!

Crazy enough, I'm not doing much differently than the VersioningIterator as it is storing the max number of versions that ti should be returning- right? And that's a scan time iterator (as well as majc/minc).

I am testing it as a scan time iterator (set on the table but using accumulo shell to scan). Perhaps I should force a couple compactions and see what's left afterwards.

On Jan 3, 2013, at 5:53 PM, John Vines wrote:

> 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 <[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
>