Re: Compression of full-page-writes

On Sun, Dec 7, 2014 at 9:30 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> * parameter should be SUSET - it doesn't *need* to be set only at
> server start since all records are independent of each other

Why not USERSET? There's no point in trying to prohibit users from
doing things that will cause bad performance because they can do that
anyway.

> * ideally we'd like to be able to differentiate the types of usage.
> which then allows the user to control the level of compression
> depending upon the type of action. My first cut at what those settings
> should be are ALL > LOGICAL > PHYSICAL > VACUUM.
>
> VACUUM - only compress while running vacuum commands
> PHYSICAL - only compress while running physical DDL commands (ALTER
> TABLE set tablespace, CREATE INDEX), i.e. those that wouldn't
> typically be used for logical decoding
> LOGICAL - compress FPIs for record types that change tables
> ALL - all user commands
> (each level includes all prior levels)

Interesting idea, but what evidence do we have that a simple on/off
switch isn't good enough?

> * name should not be wal_compression - we're not compressing all wal
> records, just fpis. There is no evidence that we even want to compress
> other record types, nor that our compression mechanism is effective at
> doing so. Simple => keep name as compress_full_page_writes

Quite right.

--
Robert Haas
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