Hi, On 2016/02/29 18:05, Thomas Munro wrote: > On Mon, Feb 29, 2016 at 9:05 PM, Amit Langote wrote: >> + servers. A transaction that is run with >> <varname>causal_reads</> set >> + to <literal>on</> is guaranteed either to see the effects of all >> + completed transactions run on the primary with the setting on, or >> to >> + receive an error "standby is not available for causal reads". >> >> "A transaction that is run" means "A transaction that is run on a >> standby", right? > > Well, it could be any server, standby or primary. Of course standbys > are the interesting case since it it was already true that if you run > two sequential transactions run on the primary, the second can see the > effect of the first, but I like the idea of a general rule that > applies anywhere, allowing you not to care which server it is.
I meant actually in context of that sentence only. >> By the way, is there some discussion in our existing >> documentation to refer to about causal consistency in single node case? I >> don't know maybe that will help ease into the new feature. Grepping the >> existing source tree doesn't reveal the term "causal", so maybe even a >> single line in the patch mentioning "single node operation trivially >> implies (or does it?) causal consistency" would help. Thoughts? > > Hmm. Where should such a thing go? I probably haven't introduced the > term well enough. I thought for a moment about putting something > here: > > http://www.postgresql.org/docs/devel/static/sql-commit.html > > "All changes made by the transaction become visible to others ..." -- > which others? But I backed out, that succinct account of COMMIT is 20 > years old, and in any case visibility is tied to committing, not > specifically to the COMMIT command. But perhaps this patch really > should include something there that refers back to the causal reads > section. I see. I agree this is not exactly material for the COMMIT page. Perhaps somewhere under "Chapter 13. Concurrency Control" with cross-reference to/from "25.5. Hot Standby". Might be interesting to hear from others as well. Thanks, Amit -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers