Re: Sync vs Flush
Makes sense, thanks! On Thu, Jul 2, 2020 at 15:29 Tom Lane wrote: > =?UTF-8?B?SmFrYSBKYW7EjWFy?= writes: > > What is a common situation for using Flush instead of Sync? > > When would you need and wait for the output, get an error, yet still > > proceed to send further messages that you would want the server to > ignore? > > The only case I can think of offhand is bursting some time-consuming > queries to the server, that is sending this all at once: > >Execute, Flush, Execute, Flush, Execute, Flush, Execute, Sync > > This presumes that, if an earlier query fails, you want the rest > to be abandoned; else you'd use Syncs instead. But if you leave > out the Flushes then you won't see the tail end of (or indeed > maybe none of) the output of an earlier query until a later query > fills the server's output buffer. So if you're hoping to overlap > the client's processing with the server's you want the extra flushes. > > regards, tom lane >
Re: Sync vs Flush
=?UTF-8?B?SmFrYSBKYW7EjWFy?= writes: > What is a common situation for using Flush instead of Sync? > When would you need and wait for the output, get an error, yet still > proceed to send further messages that you would want the server to ignore? The only case I can think of offhand is bursting some time-consuming queries to the server, that is sending this all at once: Execute, Flush, Execute, Flush, Execute, Flush, Execute, Sync This presumes that, if an earlier query fails, you want the rest to be abandoned; else you'd use Syncs instead. But if you leave out the Flushes then you won't see the tail end of (or indeed maybe none of) the output of an earlier query until a later query fills the server's output buffer. So if you're hoping to overlap the client's processing with the server's you want the extra flushes. regards, tom lane
Re: Sync vs Flush
Hehe, that's exactly what I am doing, which is why I thought of just sending two Syncs. Good to hear it's OK. >From reading the Extended query protocol docs, I somehow got the impression that you need to do everything within one cycle, and send Sync only at the end of the cycle: - "The extended query protocol breaks down the above-described simple query protocol into multiple steps." - "[Only] At completion of each series of extended-query messages, the frontend should issue a Sync message." - "A Flush [and not Sync] must be sent [...] if the frontend wishes to examine the results of that command before issuing more commands." - "The simple Query message is approximately equivalent to the series Parse, Bind, portal Describe, Execute, Close, Sync." What is a common situation for using Flush instead of Sync? When would you need and wait for the output, get an error, yet still proceed to send further messages that you would want the server to ignore? Jaka On Thu, Jul 2, 2020 at 12:41 PM Tom Lane wrote: > =?UTF-8?B?SmFrYSBKYW7EjWFy?= writes: > > For an extended query that needs to get parameter types before sending > > them, is there a difference in doing: > > > Parse, Describe statement, Flush, Bind, Execute, Sync > > vs > > Parse, Describe statement, Sync, Bind, Execute, Sync > > Sync is a resync point after an error, so the real question is what > you want to have happen if you get some kind of error during the Parse. > If you expect that the app wouldn't proceed with issuing Bind/Execute > then you want to do it the second way. > > I suppose you could do > > Send Parse/Describe/Flush > Read results > If OK: >Send Bind/Execute/Sync > else: >Send Sync# needed to get back to normal state > > but that doesn't sound all that convenient. > > regards, tom lane >
Re: Sync vs Flush
=?UTF-8?B?SmFrYSBKYW7EjWFy?= writes: > For an extended query that needs to get parameter types before sending > them, is there a difference in doing: > Parse, Describe statement, Flush, Bind, Execute, Sync > vs > Parse, Describe statement, Sync, Bind, Execute, Sync Sync is a resync point after an error, so the real question is what you want to have happen if you get some kind of error during the Parse. If you expect that the app wouldn't proceed with issuing Bind/Execute then you want to do it the second way. I suppose you could do Send Parse/Describe/Flush Read results If OK: Send Bind/Execute/Sync else: Send Sync# needed to get back to normal state but that doesn't sound all that convenient. regards, tom lane
