Hi! Please, do not use top-posting, i.e. reply style where you quote whole message under your response. It makes reading of archives terse.
> 24 июня 2019 г., в 7:53, Binguo Bao <djydewang@gmail.com> написал(а): > >> This is not correct: L bytes of compressed data do not always can be decoded into at least L bytes of data. At worst we have one control byte per 8 bytes of literal bytes. This means at most we need (L*9 + 8) / 8 bytes with current pglz format. > > Good catch! I've corrected the related code in the patch. > ... > <0001-Optimize-partial-TOAST-decompression-2.patch>
I've took a look into the code. I think we should extract function for computation of max_compressed_size and put it somewhere along with pglz code. Just in case something will change something about pglz so that they would not forget about compression algorithm assumption.
Also I suggest just using 64 bit computation to avoid overflows. And I think it worth to check if max_compressed_size is whole data and use min of (max_compressed_size, uncompressed_data_size).
Also you declared needsize and max_compressed_size too far from use. But this will be solved by function extraction anyway.
Thanks!
Best regards, Andrey Borodin.
Thanks for the suggestion.
I've extracted function for computation for max_compressed_size and put the function into pg_lzcompress.c.
