On Tue, May 11, 2021 at 4:50 PM Amul Sul <sula...@gmail.com> wrote: > > On Tue, May 11, 2021 at 4:13 PM Dilip Kumar <dilipbal...@gmail.com> wrote: > > I might be missing something, but assume the behavior should be like this > > > > 1. If the state is getting changed from WALPROHIBIT_STATE_READ_WRITE > > -> WALPROHIBIT_STATE_READ_ONLY, then as soon as the backend process > > the barrier, we can immediately abort any read-write transaction(and > > stop allowing WAL writing), because once we ensure that all session > > has responded that now they have no read-write transaction then we can > > safely change the state from WALPROHIBIT_STATE_GOING_READ_ONLY to > > WALPROHIBIT_STATE_READ_ONLY. > > > > Yes, that's what the current patch is doing from the first patch version. > > > 2. OTOH, if we are changing from WALPROHIBIT_STATE_READ_ONLY -> > > WALPROHIBIT_STATE_READ_WRITE, then we don't need to allow the backend > > to consider the system as read-write, instead, we should wait until > > the shared state is changed to WALPROHIBIT_STATE_READ_WRITE. > > > > I am sure that only not enough will have the same issue where > LocalXLogInsertAllowed gets set the same as the read-only as described in > my previous reply.
Okay, but while browsing the code I do not see any direct if condition based on the "LocalXLogInsertAllowed" variable, can you point me to some references? I only see one if check on this variable and that is in XLogInsertAllowed() function, but now in XLogInsertAllowed() function, you are already checking IsWALProhibited. No? > > Other than this point, I think the state names READ_ONLY, READ_WRITE > > are a bit confusing no? because actually, these states represent > > whether WAL is allowed or not, but READ_ONLY, READ_WRITE seems like we > > are putting the system under a Read-only state. For example, if you > > are doing some write operation on an unlogged table will be allowed, I > > guess because that will not generate the WAL until you commit (because > > commit generates WAL) right? so practically, we are just blocking the > > WAL, not the write operation. > > > > This read-only and read-write are the wal prohibited states though we > are using for read-only/read-write system in the discussion and the > complete macro name is WALPROHIBIT_STATE_READ_ONLY and > WALPROHIBIT_STATE_READ_WRITE, I am not sure why that would make > implementation confusing. Fine, I am not too particular about these names. -- Regards, Dilip Kumar EnterpriseDB: http://www.enterprisedb.com
