When the dictionary is <= 8 bytes, no data is loaded from the dictionary.
In this case the repcodes weren't set, because they were inserted after the
size check. Fix this problem in general by first setting the cdict state to
a clean state of an empty dictionary, then filling the state from there.
Produces 3 statistics for ongoing frame compression :
- ingested
- consumed (effectively compressed)
- produced
Ingested can be larger than consumed due to buffering effect.
For the time being, this patch mostly fixes the % ratio issue,
since it computes consumed / produced,
instead of ingested / produced.
That being said, update is not "smooth",
because on a slow enough setting,
fileio spends most of its time waiting for a worker to complete its job.
This could be improved thanks to more granular flushing
i.e. start flushing before ongoing job is fully completed.
would create too large buffers,
since default job size == window size * 4.
This would crash on 32-bit systems.
Also : jobSize being a 32-bit unsigned, it cannot be >= 4 GB,
so the formula was failing for large window sizes >= 1 GB.
Fixed now : max job Size is 2 GB, whatever the window size.
this happened on 32-bits build when requiring a too large input buffer,
typically on wlog=29, creating jobs of 2 GB size.
also : zstd32 now compiles with multithread support enabled by default
(can be disabled with HAVE_THREAD=0)
Shaves 492,076 B off of the `ZSTD_CDict`.
The size of a `ZSTD_CDict` created from a 112,640 B dictionary is:
| Level | Before (B) | After (B) |
|-------|------------|-----------|
| 1 | 648,448 | 156,412 |
| 3 | 1,140,008 | 647,932 |
This new parameter makes it possible to call
streaming ZSTDMT with a single thread set
which is non blocking.
It makes it possible for the main thread to do other tasks in parallel
while the worker thread does compression.
Typically, for zstd cli, it means it can do I/O stuff.
Applied within fileio.c, this patch provides non-negligible gains during compression.
Tested on my laptop, with enwik9 (1000000000 bytes) : time zstd -f enwik9
With traditional single-thread blocking mode :
real 0m9.557s
user 0m8.861s
sys 0m0.538s
With new single-worker non blocking mode :
real 0m7.938s
user 0m8.049s
sys 0m0.514s
=> 20% faster
it still fallbacks to single-thread blocking invocation
when input is small (<1job)
or when invoking ZSTDMT_compress(), which is blocking.
Also : fixed a bug in new block-granular compression routine.
Pathological samples may result in literal section being incompressible.
This case is now detected,
and literal distribution is replaced by one that can be written into the dictionary.
constants in zstd.h should not depend on MIN() macro which existence is not guaranteed.
Added a test to check the specific constants.
The test is a bit too specific.
But I have found no way to control a more generic "are all macro already defined" condition,
especially as this is a valid construction (the missing macro might be defined later, intentionnally).
in a new "custom memory allocator" paragraph
which is itself part of "memory management" category.
This makes it simpler to see the relation between the type and its usages.
It used to stop on reaching extDict, for simplification.
As a consequence, there was a small loss of performance each time the round buffer would restart from beginning.
It's not a large difference though, just several hundreds of bytes on silesia.
This patch fixes it.
now selected for levels 13, 14 and 15.
Also : dropped the requirement for monotonic memory budget increase of compression levels,,
which was required for ZSTD_estimateCCtxSize()
in order to ensure that a memory budget for level L is large enough for any level <= L.
This condition is now ensured at run time inside ZSTD_estimateCCtxSize().
we want the dictionary table to be fully sorted,
not just lazily filled.
Dictionary loading is a bit more intensive,
but it saves cpu cycles for match search during compression.
This is a pretty nice speed win.
The new strategy consists in stacking new candidates as if it was a hash chain.
Then, only if there is a need to actually consult the chain, they are batch-updated,
before starting the match search itself.
This is supposed to be beneficial when skipping positions,
which happens a lot when using lazy strategy.
The baseline performance for btlazy2 on my laptop is :
15#calgary.tar : 3265536 -> 955985 (3.416), 7.06 MB/s , 618.0 MB/s
15#enwik7 : 10000000 -> 3067341 (3.260), 4.65 MB/s , 521.2 MB/s
15#silesia.tar : 211984896 -> 58095131 (3.649), 6.20 MB/s , 682.4 MB/s
(only level 15 remains for btlazy2, as this strategy is squeezed between lazy2 and btopt)
After this patch, and keeping all parameters identical,
speed is increased by a pretty good margin (+30-50%),
but compression ratio suffers a bit :
15#calgary.tar : 3265536 -> 958060 (3.408), 9.12 MB/s , 621.1 MB/s
15#enwik7 : 10000000 -> 3078318 (3.249), 6.37 MB/s , 525.1 MB/s
15#silesia.tar : 211984896 -> 58444111 (3.627), 9.89 MB/s , 680.4 MB/s
That's because I kept `1<<searchLog` as a maximum number of candidates to update.
But for a hash chain, this represents the total number of candidates in the chain,
while for the binary, it represents the maximum depth of searches.
Keep in mind that a lot of candidates won't even be visited in the btree,
since they are filtered out by the binary sort.
As a consequence, in the new implementation,
the effective depth of the binary tree is substantially shorter.
To compensate, it's enough to increase `searchLog` value.
Here is the result after adding just +1 to searchLog (level 15 setting in this patch):
15#calgary.tar : 3265536 -> 956311 (3.415), 8.32 MB/s , 611.4 MB/s
15#enwik7 : 10000000 -> 3067655 (3.260), 5.43 MB/s , 535.5 MB/s
15#silesia.tar : 211984896 -> 58113144 (3.648), 8.35 MB/s , 679.3 MB/s
aka, almost the same compression ratio as before,
but with a noticeable speed increase (+20-30%).
This modification makes btlazy2 more competitive.
A new round of paramgrill will be necessary to determine which levels are impacted and could adopt the new strategy.
params1 was swapped with params2.
This used to be a non-issue when testing for strict equality,
but now that some tests look for "sufficient size" `<=`, order matters.
Yann Collet