Thread: 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 files > > BTW, 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 files >> >> BTW, 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. > > Ciao, > > Gerhard > > >