Re: [HACKERS] Transactions involving multiple postgres foreign servers, take 2

Hi Sawada San,

I have a couple of comments on "v27-0002-Support-atomic-commit-among-multiple-foreign-ser.patch"

1- As part of the XLogReadRecord refactoring commit the signature of XLogReadRecord was changed,
so the function call to XLogReadRecord() needs a small adjustment.

i.e. In function XlogReadFdwXactData(XLogRecPtr lsn, char **buf, int *len)
...
- record = XLogReadRecord(xlogreader, lsn, &errormsg);
+ XLogBeginRead(xlogreader, lsn)
+ record = XLogReadRecord(xlogreader, &errormsg);

2- In register_fdwxact(..) function you are setting the XACT_FLAGS_FDWNOPREPARE transaction flag
when the register request comes in for foreign server that does not support two-phase commit regardless
of the value of 'bool modified' argument. And later in the PreCommit_FdwXacts() you just error out when
"foreign_twophase_commit" is set to 'required' only by looking at the XACT_FLAGS_FDWNOPREPARE flag.
which I think is not correct.
Since there is a possibility that the transaction might have only read from the foreign servers (not capable of
handling transactions or two-phase commit) and all other servers where we require to do atomic commit
are capable enough of doing so.
If I am not missing something obvious here, then IMHO the XACT_FLAGS_FDWNOPREPARE flag should only
be set when the transaction management/two-phase functionality is not available and "modified" argument is
true in register_fdwxact()

Thanks

Best regards
Muhammad Usama
Highgo Software (Canada/China/Pakistan)

The new status of this patch is: Waiting on Author