From: | Heikki Linnakangas <heikki(at)enterprisedb(dot)com> |
---|---|
To: | Chongfeng Hu <loveminix(at)yahoo(dot)com(dot)cn> |
Cc: | pgsql-bugs(at)postgresql(dot)org |
Subject: | Re: BUG #3143: MyLastRecPtr.xlogid not updated with MyLastRecPtr.xrecoff? |
Date: | 2007-03-12 13:06:57 |
Message-ID: | 45F55071.2040906@enterprisedb.com |
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Thread: | |
Lists: | pgsql-bugs |
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
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