Re: Compressed TOAST Slicing

> On Mar 11, 2019, at 10:42 PM, Michael Paquier <michael@paquier.xyz> wrote:
>
> On Mon, Mar 11, 2019 at 08:38:56PM +0000, Regina Obe wrote:
>> I tested on windows mingw64 (as of a week ago) and confirmed the
>> patch applies cleanly and significantly faster for left, substr
>> tests than head.
>
> int32
> pglz_decompress(const char *source, int32 slen, char *dest,
> -                               int32 rawsize)
> +                               int32 rawsize, bool is_slice)
> The performance improvements are nice, but breaking a published API is
> less nice particularly since some work has been done to make pglz more
> plugabble (see 60838df9, guess how wrote that).  Could it be possible
> to rework this part please?  It's been some time since I touched this
> code, but it would be really nice if we don't have an extra parameter,
> and just not bypass the sanity checks at the end.  Using a parameter
> to bypass those checks may cause problems for future callers of it.

The sanity check is just that both buffers are completely read they reach their respective ends. With a partial buffer
onone side, that check just will definitionally not  happen when slicing (it’s not possible to know a priori what
locationin the compressed buffer corresponds to a location in the uncompressed one). I can ensure the old API still
holdsfor pglz_decompress() and add a new pglz_decompress_slice() that takes the parameter, is that sufficient? 

P.