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fix typo in segments.md

This commit is contained in:
Bingkun Guo 2015-09-11 16:32:32 -05:00
parent 252bb5a6bc
commit e222e6b86b
1 changed files with 8 additions and 8 deletions
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docs/content/design/segments.md
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@ -82,11 +82,11 @@ Note that the bitmap is different from the first two data structures:
whereas the first two grow linearly in the size of the data (in the whereas the first two grow linearly in the size of the data (in the
worst case), the size of the bitmap section is the product of data worst case), the size of the bitmap section is the product of data
size * column cardinality. Compression will help us here though size * column cardinality. Compression will help us here though
because we know that each row will have only non-zero entry in a only because we know that for each row in 'column data', there will only be a
a single bitmap. This means that high cardinality columns will have single bitmap that has non-zero entry. This means that high cardinality
extremely sparse, and therefore highly compressible, bitmaps. Druid columns will have extremely sparse, and therefore highly compressible,
exploits this using compression algorithms that are specially suited bitmaps. Druid exploits this using compression algorithms that are
for bitmaps, such as roaring bitmap compression. specially suited for bitmaps, such as roaring bitmap compression.
### Multi-value columns ### Multi-value columns
@ -121,8 +121,8 @@ data structures would now look as follows:
Note the changes to the second row in the column data and the Ke$ha Note the changes to the second row in the column data and the Ke$ha
bitmap. If a row has more than one value for a column, its entry in bitmap. If a row has more than one value for a column, its entry in
the 'column data' is an array of values. Additionally, a row with *n* the 'column data' is an array of values. Additionally, a row with *n*
values in a column columns will have *n* non-zero valued entries in values in 'column data' will have *n* non-zero valued entries in
that column's bitmaps. bitmaps.
Naming Convention Naming Convention
----------------- -----------------
@ -176,4 +176,4 @@ representing the same time interval for the same datasource may be
created. These segments will contain some partition number as part of created. These segments will contain some partition number as part of
their identifier. Sharding by dimension reduces some of the the costs their identifier. Sharding by dimension reduces some of the the costs
associated with operations over high cardinality dimensions. For more associated with operations over high cardinality dimensions. For more
information on sharding, see the ingestion documentat information on sharding, see the ingestion documentation.