On 27.06.2019 21:33, Andrey Borodin wrote:
13 мая 2019 г., в 12:14, Michael Paquier <mich...@paquier.xyz> написал(а):
Decompression can matter a lot for mostly-read workloads and
compression can become a bottleneck for heavy-insert loads, so
improving compression or decompression should be two separate
problems, not two problems linked. Any improvement in one or the
other, or even both, is nice to have.
Here's patch hacked by Vladimir for compression.
Key differences (as far as I see, maybe Vladimir will post more complete list
of optimizations):
1. Use functions instead of macro-functions: not surprisingly it's easier to
optimize them and provide less constraints for compiler to optimize.
2. More compact hash table: use indexes instead of pointers.
3. More robust segment comparison: like memcmp, but return index of first
different byte
In weighted mix of different data (same as for compression), overall speedup is
x1.43 on my machine.
Current implementation is integrated into test_pglz suit for benchmarking
purposes[0].
Best regards, Andrey Borodin.
[0] https://github.com/x4m/test_pglz
It takes me some time to understand that your memcpy optimization is
correct;)
I have tested different ways of optimizing this fragment of code, but
failed tooutperform your implementation!
Results at my computer is simlar with yours:
Decompressor score (summ of all times):
NOTICE: Decompressor pglz_decompress_hacked result 6.627355
NOTICE: Decompressor pglz_decompress_hacked_unrolled result 7.497114
NOTICE: Decompressor pglz_decompress_hacked8 result 7.412944
NOTICE: Decompressor pglz_decompress_hacked16 result 7.792978
NOTICE: Decompressor pglz_decompress_vanilla result 10.652603
Compressor score (summ of all times):
NOTICE: Compressor pglz_compress_vanilla result 116.970005
NOTICE: Compressor pglz_compress_hacked result 89.706105
But ... below are results for lz4:
Decompressor score (summ of all times):
NOTICE: Decompressor lz4_decompress result 3.660066
Compressor score (summ of all times):
NOTICE: Compressor lz4_compress result 10.288594
There is 2 times advantage in decompress speed and 10 times advantage in
compress speed.
So may be instead of "hacking" pglz algorithm we should better switch to
lz4?
--
Konstantin Knizhnik
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company
