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Update documentation for environment variable

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senhuang42 2020-09-07 18:35:46 -04:00
parent 136a0673f6
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2 changed files with 20 additions and 6 deletions
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13
programs/README.md
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@ -204,14 +204,19 @@ Benchmark arguments :
### Passing parameters through Environment Variables ### Passing parameters through Environment Variables
`ZSTD_CLEVEL` can be used to modify the default compression level of `zstd` `ZSTD_CLEVEL` can be used to modify the default compression level of `zstd`
(usually set to `3`) to another value between 1 and 19 (the "normal" range). (usually set to `3`) to another value between 1 and 19 (the "normal" range).
This can be useful when `zstd` CLI is invoked in a way that doesn't allow passing arguments. `ZSTD_NUMTHREADS` can be used to specify number of threads that `zstd` will use during compression, which by default is `1`.
This functionality only exists when `zstd` is compiled with multithread support.
The max # of threads is capped at: `ZSTDMT_NBWORKERS_MAX==200`.
This functionality can be useful when `zstd` CLI is invoked in a way that doesn't allow passing arguments.
One such scenario is `tar --zstd`. One such scenario is `tar --zstd`.
As `ZSTD_CLEVEL` only replaces the default compression level, As `ZSTD_CLEVEL` and `ZSTD_NUMTHREADS` only replace the default compression level
it can then be overridden by corresponding command line arguments. and number of threads, respectively, they can both be overridden by corresponding command line arguments:
`-#` for compression level and `-T#` for number of threads.
There is no "generic" way to pass "any kind of parameter" to `zstd` in a pass-through manner. There is no "generic" way to pass "any kind of parameter" to `zstd` in a pass-through manner.
Using environment variables for this purpose has security implications. Using environment variables for this purpose has security implications.
Therefore, this avenue is intentionally restricted and only supports `ZSTD_CLEVEL`. Therefore, this avenue is intentionally restricted and only supports `ZSTD_CLEVEL` and `ZSTD_NUMTHREADS`.
### Long distance matching mode ### Long distance matching mode
The long distance matching mode, enabled with `--long`, is designed to improve The long distance matching mode, enabled with `--long`, is designed to improve

13
programs/zstd.1.md
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@ -270,11 +270,20 @@ the last one takes effect.
Using environment variables to set parameters has security implications. Using environment variables to set parameters has security implications.
Therefore, this avenue is intentionally restricted. Therefore, this avenue is intentionally restricted.
Only `ZSTD_CLEVEL` is supported currently, for setting compression level. Only `ZSTD_CLEVEL` and `ZSTD_NUMTHREADS` are currently supported.
They set the compression level and number of threads to use during compression, respectively.
`ZSTD_CLEVEL` can be used to set the level between 1 and 19 (the "normal" range). `ZSTD_CLEVEL` can be used to set the level between 1 and 19 (the "normal" range).
If the value of `ZSTD_CLEVEL` is not a valid integer, it will be ignored with a warning message. If the value of `ZSTD_CLEVEL` is not a valid integer, it will be ignored with a warning message.
`ZSTD_CLEVEL` just replaces the default compression level (`3`). `ZSTD_CLEVEL` just replaces the default compression level (`3`).
It can be overridden by corresponding command line arguments.
`ZSTD_NUMTHREADS` can be used to set the number of threads `zstd` will attempt to use during compression.
If the value of `ZSTD_NUMTHREADS` is not a valid unsigned integer, it will be ignored with a warning message.
'ZSTD_NUMTHREADS` has a default value of (`1`), and is capped at ZSTDMT_NBWORKERS_MAX==200. `zstd` must be
compiled with multithread support for this to have any effect.
They can both be overridden by corresponding command line arguments:
`-#` for compression level and `-T#` for number of compression threads.
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