Hi,
On 06/26/2017 05:18 PM, Alexander Korotkov wrote:
Hackers,
I see that design question for PostgreSQL pluggable storages is very
hard.
IMHO it's mostly expected to be hard.
Firstly, PostgreSQL is a mature product with many advanced features, and
reworking a low-level feature without breaking something on top of it is
hard by definition.
Secondly, project policies and code quality requirements set the bar
very high too, I think.
> BTW, I think it worth analyzing existing use-cases of pluggable
storages. I think that the most famous DBMS with pluggable storage API
is MySQL. This why I decided to start with it. I've added
MySQL/MariaDB section on wiki page.
https://wiki.postgresql.org/wiki/Future_of_storage#MySQL.2FMariaDB
It appears that significant part of MySQL storage engines are misuses.
MySQL lacks of various features like FDWs or writable views and so on.
This is why developers created a lot of pluggable storages for that
purposes. We definitely don't want something like this in PostgreSQL
now. I created special resume column where I expressed whether it
would be nice to have something like this table engine in PostgreSQL.
I don't want to discourage you, but I'm not sure how valuable this is.
I agree it's valuable to have a an over-view of use cases for pluggable
storage, but I don't think we'll get that from looking at MySQL. As you
noticed, most of the storage engines are misuses, so it's difficult to
learn anything valuable from them. You can argue that using FDWs to
implement alternative storage engines is a misuse too, but at least that
gives us a valid use case (columnar storage implemented using FDW).
If anything, the MySQL storage engines should serve as a cautionary tale
how not to do things - there's also a plenty of references in the MySQL
"Restrictions and Limitations" section of the manual:
https://downloads.mysql.com/docs/mysql-reslimits-excerpt-5.7-en.pdf
regards
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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