Re: A separate table level option to control compression

On Wed, Feb 6, 2019 at 4:32 PM Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com> wrote:
>
> Hello,
>
> Currently either the table level option `toast_tuple_target` or the compile time default `TOAST_TUPLE_TARGET` is used to decide whether a new tuple should be compressed or not. While this works reasonably well for most situations, at times the user may not want to pay the overhead of toasting, yet take benefits of inline compression.
>
> I would like to propose a new table level option, compress_tuple_target, which can be set independently of toast_tuple_target, and is checked while deciding whether to compress the new tuple or not.
>
> For example,
>
> CREATE TABLE compresstest250 (a int, b text) WITH (compress_tuple_target = 250);
> CREATE TABLE compresstest2040 (a int, b text) WITH (compress_tuple_target = 2040);
>
> -- shouldn't get compressed nor toasted
> INSERT INTO compresstest250 VALUES (1, repeat('1234567890',20));
>
> -- should get compressed, but not toasted
> INSERT INTO compresstest250 VALUES (2, repeat('1234567890',30));
>
> -- shouldn't get compressed nor toasted
> INSERT INTO compresstest2040 VALUES (1, repeat('1234567890',20));
> INSERT INTO compresstest2040 VALUES (2, repeat('1234567890',30));
>
> Without this patch, the second INSERT will not compress the tuple since its length is less than the toast threshold. With the patch and after setting table level option, one can compress such tuples.
>
> The attached patch implements this idea.
>

I like this idea.

The patch seems to need update the part describing on-disk toast
storage in storage.sgml.

Regards,

--
Masahiko Sawada
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center