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updated LDM documentation

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Yann Collet 2025-02-07 17:15:24 -08:00 committed by Yann Collet
parent f26cc54f37
commit bf218c142a
2 changed files with 20 additions and 18 deletions
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11
programs/fileio.c
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@ -1100,11 +1100,12 @@ static void FIO_adjustParamsForPatchFromMode(FIO_prefs_t* const prefs,
FIO_setLdmFlag(prefs, 1);
}
if (cParams.strategy >= ZSTD_btopt) {
DISPLAYLEVEL(3, "[Optimal parser notes] Consider the following to improve patch size at the cost of speed:\n");
DISPLAYLEVEL(3, "- Use --single-thread mode in the zstd cli\n");
DISPLAYLEVEL(3, "- Set a larger targetLength (e.g. --zstd=targetLength=4096)\n");
DISPLAYLEVEL(3, "- Set a larger chainLog (e.g. --zstd=chainLog=%u)\n", ZSTD_CHAINLOG_MAX);
DISPLAYLEVEL(3, "Also consider playing around with searchLog and hashLog\n");
DISPLAYLEVEL(4, "[Optimal parser notes] Consider the following to improve patch size at the cost of speed:\n");
DISPLAYLEVEL(4, "- Set a larger targetLength (e.g. --zstd=targetLength=4096)\n");
DISPLAYLEVEL(4, "- Set a larger chainLog (e.g. --zstd=chainLog=%u)\n", ZSTD_CHAINLOG_MAX);
DISPLAYLEVEL(4, "- Set a larger LDM hashLog (e.g. --zstd=ldmHashLog=%u)\n", ZSTD_LDM_HASHLOG_MAX);
DISPLAYLEVEL(4, "- Set a smaller LDM rateLog (e.g. --zstd=ldmHashRateLog=%u)\n", ZSTD_LDM_HASHRATELOG_MIN);
DISPLAYLEVEL(4, "Also consider playing around with searchLog and hashLog\n");
}
}

27
programs/zstd.1.md
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@ -455,6 +455,17 @@ The list of available _options_:
Value 0 is special and means "default": _ovlog_ is automatically determined by `zstd`.
In which case, _ovlog_ will range from 6 to 9, depending on selected _strat_.
- `ldmHashRateLog`=_lhrlog_, `lhrlog`=_lhrlog_:
Specify the frequency of inserting entries into the long distance matching
hash table.
This option is ignored unless long distance matching is enabled.
Larger values will improve compression speed. Deviating far from the
default value will likely result in a decrease in compression ratio.
The default value varies between 4 and 8, depending on `strategy`.
- `ldmHashLog`=_lhlog_, `lhlog`=_lhlog_:
Specify the maximum size for a hash table used for long distance matching.
@ -463,7 +474,7 @@ The list of available _options_:
Bigger hash tables usually improve compression ratio at the expense of more
memory during compression and a decrease in compression speed.
The minimum _lhlog_ is 6 and the maximum is 30 (default: 20).
The minimum _lhlog_ is 6 and the maximum is 30 (default: `windowLog - ldmHashRateLog`).
- `ldmMinMatch`=_lmml_, `lmml`=_lmml_:
Specify the minimum searched length of a match for long distance matching.
@ -472,7 +483,7 @@ The list of available _options_:
Larger/very small values usually decrease compression ratio.
The minimum _lmml_ is 4 and the maximum is 4096 (default: 64).
The minimum _lmml_ is 4 and the maximum is 4096 (default: 32 to 128, depending on `strategy`).
- `ldmBucketSizeLog`=_lblog_, `lblog`=_lblog_:
Specify the size of each bucket for the hash table used for long distance
@ -483,18 +494,8 @@ The list of available _options_:
Larger bucket sizes improve collision resolution but decrease compression
speed.
The minimum _lblog_ is 1 and the maximum is 8 (default: 3).
The minimum _lblog_ is 1 and the maximum is 8 (default: 4 to 8, depending on `strategy`).
- `ldmHashRateLog`=_lhrlog_, `lhrlog`=_lhrlog_:
Specify the frequency of inserting entries into the long distance matching
hash table.
This option is ignored unless long distance matching is enabled.
Larger values will improve compression speed. Deviating far from the
default value will likely result in a decrease in compression ratio.
The default value is `wlog - lhlog`.
### Example
The following parameters sets advanced compression options to something