Re: Proposal: custom compression methods

On 12/14/15 01:50, Craig Ringer wrote:

> pg_upgrade means you can't just redefine the current toast bits so the
> compressed bit means "data is compressed, check first byte of varlena data
> for algorithm" because existing data won't have that, the first byte will
> be the start of the compressed data stream.

Is there any small sequence of initial bytes you wouldn't ever see in PGLZ
output?  Either something invalid, or something obviously nonoptimal
like run(n,'A')||run(n,'A') where PGLZ would have just output run(2n,'A')?

-Chap