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Change the LZO testing option to be a bool on/off instead of taking a confusing parameter.

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Make the lzo testing message simpler and only appear when max verbose mode is enabled.
This commit is contained in:
Con Kolivas 2011-02-23 01:15:18 +11:00
parent fa34905d9d
commit 94673d3fe3
9 changed files with 37 additions and 75 deletions
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@ -262,41 +262,13 @@ cpu process scheduler how to prioritise workloads, and if your application is
the _only_ thing running it will be no faster at nice -20 nor will it be any
slower at +19.
Q. What is the Threshold option, -T ## (1-10)?
A. It is for adjusting the sensitivity of the LZO test that is used when LZMA
compression is selected. When highly random or already-compressed data chunks
are evaluated for LZMA compression, sometimes LZO compression actually will
create a larger chunk than the original.
The Threshold is used to determine a minimum compression amount relative to
the size of the data being evaluated. A value of 1 is the default. This
means that the compression threshold amount is >0% of the size of the
original data. If the threshold is not achieved, the LZMA compression will not
be done and the chunk will not be compressed. Values can be from 0 (bypass the
test) to 10 (maximum compression efficiency expected). The following table can
be used.
For LZO compressor test
T value Compression % Compression Ratio
0 Ignored
1 0-5% 1.00-1.05 very low compression expected
2 5-10% 1.05-1.10 default value
3 10-20% 1.12-1.25
4 20-30% 1.25-1.43
5 30-40% 1.43-1.66
6 40-50% 1.66-2.00
7 50-60% 2.00-2.50
8 60-70% 2.50-3.33
9 70-80% 3.33-5.00
10 80+% 5x+
Whenever the data chunk does not compress to the Threshold value, no LZMA
compression will be attempted. For example, if you select -T 5, LZMA
compression will be performed if the projected compression ratio is
less than 1.43. Otherwise, data will be written in rzip format. Setting
a very high T value will result in a lot of uncompressed data in the lrzip
file. However, a lot of time will be saved. For most people you shouldn't ever
need to touch this.
Q. What is the LZO Testing option, -T?
A. LZO testing is normally performed for the slower back-end compression of LZMA
and ZPAQ. The reasoning is that if it is completely incompressible by LZO then
it will also be incompressible by them. Thus if a block fails to be compressed
by the very fast LZO, lrzip will not attempt to compress that block with the
slower compressor, thereby saving time. If this option is enabled, it will
bypass the LZO testing and attempt to compress each block regardless.
Q. Compression and decompression progress on large archives slows down and
speeds up. There's also a jump in the percentage at the end?