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From "Adam Fuchs (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-652) support block-based filtering within RFile
Date Fri, 06 Jul 2012 17:07:34 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-652?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13408156#comment-13408156
] 

Adam Fuchs commented on ACCUMULO-652:
-------------------------------------

Status:
* RFile index now includes block stats for column visibility and overall timestamp range
* System-level iterators and Filters now implement the pass-through optional filter interface
(Filterer)
* ColumnVisibility has been updated to support "or" and "and" operations, and some basic simplifications
to save space
* Unit tests exist and succeed for new MultiLevelIndex and RFile implementations

Remaining work:
# Test backwards compatibility of RFile running on previous index versions
# Write a functional test that only works if the block stat filtering is in place for both
timestamp range and column visibility filters
# Run continuous ingest and wikisearch ingest performance comparisons between the 652 branch
and trunk
# Plumb in the new aggregate column visibility size limit variable
# Use a better encoding for aggregate column visibilities to save space in the index blocks
# Need a better name for the Filterer interface so as not to confuse it with Filter
# Need to handle the case in which RFile Readers are reused between scans (or make this contingent
on them not being reused)
# As Todd suggests, we should look into extending the block stats that are collected to include
basic information about included column qualifiers, values, and maybe column families.
# For future extensibility and backwards compatibility, we should look into abstracting the
block stats provider and making it pluggable
                
> support block-based filtering within RFile
> ------------------------------------------
>
>                 Key: ACCUMULO-652
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-652
>             Project: Accumulo
>          Issue Type: Bug
>            Reporter: Adam Fuchs
>            Assignee: Adam Fuchs
>
> If we keep some stats about what is in an RFile block, we might be able to efficiently
[O(log N)], with high probability, implement filters that currently require linear table scans.
Two use cases of this include timestamp range filtering (i.e. give me everything from last
Tuesday) and cell-level security filtering (i.e. give me everything that I can see with my
authorizations).
> For the timestamp range filter, we can keep minimum and maximum timestamps across all
keys used in a block within the index entry for that block. For the cell-level security filter,
we can keep an aggregate label. This could be done using a simplified disjunction of all of
the labels in the block. The extra block statistics information can propagate up the index
hierarchy as well, giving nice performance characteristics for finding the next matching entry
in a file.
> In general, this is a heuristic technique that is good if data tends to naturally cluster
in blocks with respect to the way it is queried. Testing its efficacy will require closely
emulating real-world use cases -- tests like the continuous ingest test will not be sufficient.
We will have to test for a few things:
> # The cost for storing the extra stats in the index are not too expensive.
> # The performance benefit for common use cases is significant.
> # We shouldn't introduce any unacceptable worst-case behavior, like bloating the index
to ridiculous proportions for any data set.
> Eventually this will all need to be exposed through the Iterator API to be useful, which
will be another ticket. 

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