Re: [REVIEW] Re: Compression of full-page-writes

On Mon, Jan 5, 2015 at 10:29 PM, Fujii Masao <masao.fujii@gmail.com> wrote:
> On Sun, Dec 28, 2014 at 10:57 PM, Michael Paquier wrote:
> The patch 1 cannot be applied to the master successfully because of
> recent change.
Yes, that's caused by ccb161b. Attached are rebased versions.

>> - The real stuff comes with patch 2, that implements the removal of
>> PGLZ_Header, changing the APIs of compression and decompression to pglz to
>> not have anymore toast metadata, this metadata being now localized in
>> tuptoaster.c. Note that this patch protects the on-disk format (tested with
>> pg_upgrade from 9.4 to a patched HEAD server). Here is how the APIs of
>> compression and decompression look like with this patch, simply performing
>> operations from a source to a destination:
>> extern int32 pglz_compress(const char *source, int32 slen, char *dest,
>>                           const PGLZ_Strategy *strategy);
>> extern int32 pglz_decompress(const char *source, char *dest,
>>                           int32 compressed_size, int32 raw_size);
>> The return value of those functions is the number of bytes written in the
>> destination buffer, and 0 if operation failed.
>
> So it's guaranteed that 0 is never returned in success case? I'm not sure
> if that case can really happen, though.
This is an inspiration from lz4 APIs. Wouldn't it be buggy for a
compression algorithm to return a size of 0 bytes as compressed or
decompressed length btw? We could as well make it return a negative
value when a failure occurs if you feel more comfortable with it.
--
Michael