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Erschienen in:
2010 | OriginalPaper | Buchkapitel
Join Directly on Heavy-Weight Compressed Data in Column-Oriented Database
verfasst von : Gan Liang, Li RunHeng, Jia Yan, Jin Xin
Erschienen in: Web-Age Information Management
Verlag: Springer Berlin Heidelberg
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Operating directly on compressed data can decrease CPU costs. Many light-weight compressions, such as run-length encoding and bit-vector encoding, can gain this benefit easily. Heavy-Weight Lempel-Ziv (LZ) has no method to operate directly on compressed data. We proposed a join algorithm,
LZ join
, which join two relations
R
and
S
directly on compressed data when decoding. Regard
R
as probe table and
S
as build table,
R
is encoded by LZ. When
R
probing
S
,
LZ join
decreases the join cost by using
cached results
(previous join results of IDs in
R’
s LZ dictionary window when decoder find that the same
R
’s ID sequence in window).
LZ join
combines decoding and join phase into one, which reduces the memory usage for decoding the whole
R
and CPU overhead for probing those
cached results
. Our analysis and experiments show that
LZ join
is better in some cases, the more compression ratio the better.