On 5 April 2016 at 11:18, Fujii Masao <masao.fu...@gmail.com> wrote:
> > 1. Header comments in syncrep.c need changes, not just additions. > > Okay, will consider this later. And I'd appreciate if you elaborate what > changes are necessary specifically. Some of the old header comments are now wrong. > > 2. We need tests to ensure that k >=1 and k<=N > > The changes to replication test framework was included in the patch before, > but I excluded it from the patch because I'd like to commit the core part > of > the patch first. Will review the test part later. I meant tests of setting the parameters, not tests of the feature itself. > > > > 3. There should be a WARNING if k == N to say that we don't yet provide a > > level to give Apply consistency. (I mean if we specify 2 (n1, n2) or > 3(n1, > > n2, n3) etc > > Sorry I failed to get your point. Could you tell me what Apply consistency > and why we cannot provide it when k = N? > > > 4. How does it work? > > It's pretty strange, but that isn't documented anywhere. It took me a > while > > to figure it out even though I know that code. My thought is its a lot > > slower than before, which is a concern when we know by definition that k > >=2 > > for the new feature. I was going to mention the fact that this code only > > needs to be executed by standbys mentioned in s_s_n, so we can avoid > > overhead and contention for async standbys (But Masahiko just mentioned > that > > also). > > Unless I'm missing something, the patch already avoids the overhead > of async standbys. Please see the top of SyncRepReleaseWaiters(). > Since async standbys exit at the beginning of SyncRepReleaseWaiters(), > they don't need to perform any operations that the patch adds > (e.g., find out which standbys are synchronous). > I was thinking about the overhead of scanning through the full list of WALSenders for each message, when it is a sync standby. -- Simon Riggs http://www.2ndQuadrant.com/ <http://www.2ndquadrant.com/> PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
