On 2019-Sep-29, Amit Kapila wrote: > On Sun, Sep 29, 2019 at 12:39 AM Tomas Vondra <tomas.von...@2ndquadrant.com> > wrote:
> > So that's what I did in the attached patch - I've renamed the GUC to > > logical_decoding_work_mem, detached it from m_w_m and set the default to > > 64MB (i.e. the same default as m_w_m). > > Fair enough, let's not argue more on this unless someone else wants to > share his opinion. I just read this part of the conversation and I agree that having a separate GUC with its own value independent from other GUCs is a good solution. Tying it to m_w_m seemed reasonable, but it's true that people frequently set m_w_m very high, and it would be undesirable to propagate that value to logical decoding memory usage. I wonder what would constitute good advice on how to set this value, I mean what is the metric that the user needs to be thinking about. Is it the total of memory required to keep all concurrent write transactions in memory? (Quick example: if you do 2048 wTPS and each transaction lasts 1s, and each transaction does 1kB of logically-decoded changes, then ~2MB are sufficient for the average case. Is that correct? I *think* that full-page images do not count, correct? With these things in mind users could go through pg_waldump output and figure out what to set the value to.) -- Álvaro Herrera https://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
