PostgreSQL MVCC and alternative REDO implementation - my thoughts
Hello,
I just read that blog article and I think switching to REDO logic is not
a good idea.
REDO has the following disadvantages, think of the following scenario:
Delete a lot of rows having 1 petabyte of data.
1.) PostgreSQL: has just do mark the rows as deleted, afterwards they
have to be cleaned up by (auto)vacuum. No data has to be written! Will
be quite fast.
2.) REDO logic: The deleted 1 petabyte of data (!) has to written for
crash consistency reasons at least into REDO files. And that might take
time, hours, days, weeks, month.
So please don't give up the implementation of PostgreSQL MVCC.
https://wiki.postgresql.org/wiki/MVCC
What's the plan?
Thank you.
Ciao,
Gerhard
El 18/11/18 a las 04:49, Gerhard Wiesinger escribió:
Hello,
I just read that blog article and I think switching to REDO logic is not
a good idea.
I think you got it the other way around. Postgres implementes REDO, that
is, move forward by REDOing the changes which are stored in WAL files
BTW, could you point us to the blog you read this?
Maybe you got REDO and UNDO mixed up.
Saludos,
--
Martín Marqués http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
On 18.11.2018 12:14, Martín Marqués wrote:
El 18/11/18 a las 04:49, Gerhard Wiesinger escribió:
Hello,
I just read that blog article and I think switching to REDO logic is not
a good idea.I think you got it the other way around. Postgres implementes REDO, that
is, move forward by REDOing the changes which are stored in WAL filesBTW, could you point us to the blog you read this?
Maybe you got REDO and UNDO mixed up.
Yes, I ment UNDO ...
Link is here:
https://severalnines.com/blog/five-cool-things-i-learned-postgresql-conference-europe-2018
sunday morning, too early :-)
Ciao,
Gerhard
On 18/11/18 2:04 μ.μ., Gerhard Wiesinger wrote:
On 18.11.2018 12:14, Martín Marqués wrote:
El 18/11/18 a las 04:49, Gerhard Wiesinger escribió:
Hello,
I just read that blog article and I think switching to REDO logic is
not
a good idea.I think you got it the other way around. Postgres implementes REDO, that
is, move forward by REDOing the changes which are stored in WAL filesBTW, could you point us to the blog you read this?
Maybe you got REDO and UNDO mixed up.
Yes, I ment UNDO ...
Link is here:
https://severalnines.com/blog/five-cool-things-i-learned-postgresql-conference-europe-2018
sunday morning, too early :-)
In this blog I had the role of the reporter for the event :)
When and if this makes it to the core, both heaps will be supported.
Nevertheless this sounds exciting feature to have, however lots of work
must be done before PostgreSQL is able to adopt this in an elegant manner.
Show quoted text
Ciao,
Gerhard