Re: BUG #3143: MyLastRecPtr.xlogid not updated with MyLastRecPtr.xrecoff?

Chongfeng Hu wrote:
> However, in file src/backend/access/transam/xact.c, on line 1778, I saw the
> following code:
>
>     /* Break the chain of back-links in the XLOG records I output */
>     MyLastRecPtr.xrecoff = 0;
>     MyXactMadeXLogEntry = false;
>     MyXactMadeTempRelUpdate = false;
>
> It only updated xrecoff, but not xlogid. This might cause serious problems,
> because xlogid is still pointing to an old file, while xrecoff is pointing
> to a new offset. It might read incorrect records.

No, that's actually ok. MyLastRecPtr is used to check if the current
transaction has made any transaction-controlled WAL records. If
MyLastRecPtr.xrecoff == 0, it hasn't, otherwise it has. All readers of
the variable just check for MyLastRecPtr.xrecoff == 0, so the above is OK.

I agree that it is a bit misleading, though. A boolean
"MyXactMadeTransactionControlledXlogEntry", like the
"MyXactMadeXLogEntry" and "MyXactMadeTempRelupdate" variables would be
cleaner.

--
   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com