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Adding documentation for shrink flag PR #1656

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Tyler Tran
2019-07-22 16:33:22 -07:00
parent be3d2e2de8
commit 02da4497f0
3 changed files with 15 additions and 6 deletions
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programs/zstd.1.md
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@@ -244,13 +244,15 @@ Compression of small files similar to the sample set will be greatly improved.
This compares favorably to 4 bytes default.
However, it's up to the dictionary manager to not assign twice the same ID to
2 different dictionaries.
* `--train-cover[=k#,d=#,steps=#,split=#]`:
* `--train-cover[=k#,d=#,steps=#,split=#,shrink[=#]]`:
Select parameters for the default dictionary builder algorithm named cover.
If _d_ is not specified, then it tries _d_ = 6 and _d_ = 8.
If _k_ is not specified, then it tries _steps_ values in the range [50, 2000].
If _steps_ is not specified, then the default value of 40 is used.
If _split_ is not specified or split <= 0, then the default value of 100 is used.
Requires that _d_ <= _k_.
If _shrink_ flag is not used, then the default value for _shrinkDict_ of 0 is used.
If _shrink_ is not specified, then the default value for _shrinkDictMaxRegression_ of 1 is used.
Selects segments of size _k_ with highest score to put in the dictionary.
The score of a segment is computed by the sum of the frequencies of all the
@@ -262,6 +264,9 @@ Compression of small files similar to the sample set will be greatly improved.
If _split_ is 100, all input samples are used for both training and testing
to find optimal _d_ and _k_ to build dictionary.
Supports multithreading if `zstd` is compiled with threading support.
Having _shrink_ enabled takes a truncated dictionary of minimum size and doubles
in size until compression ratio of the truncated dictionary is at most
_shrinkDictMaxRegression_% worse than the compression ratio of the largest dictionary.
Examples:
@@ -275,6 +280,10 @@ Compression of small files similar to the sample set will be greatly improved.
`zstd --train-cover=k=50,split=60 FILEs`
`zstd --train-cover=shrink FILEs`
`zstd --train-cover=shrink=2 FILEs`
* `--train-fastcover[=k#,d=#,f=#,steps=#,split=#,accel=#]`:
Same as cover but with extra parameters _f_ and _accel_ and different default value of split
If _split_ is not specified, then it tries _split_ = 75.