On Fri, Sep 12, 2014 at 4:55 PM, Heikki Linnakangas
<hlinnakan...@vmware.com> wrote:
> I haven't looked at those places closely, but it seems possible that at
> least some of those variables are supposed to be initialized to a value
> smaller than any valid WAL position, rather than just Invalid. In other
> words, if we defined InvalidXLogRecPtr as INT64_MAX rather than 0, we would
> still want those variables to be initialized to zero. As I said, I didn't
> check the code, but before we change those that ought to be checked.
Ah, OK. I just had a look at that, and receivedUpto and lastComplaint
in xlog.c need to use the lowest pointer value possible as they do a
couple of comparisons with other positions. This is as well the case
of sentPtr in walsender.c. However, that's not the case of writePtr
and flushPtr in walreceiver.c as those positions are just used for
direct comparison with LogstreamResult, so we could use
InvalidXLogRecPtr in this case.
What do you think of the addition of a #define for the lowest possible
XLOG location pointer? I've wanted that as well a couple of times when
working on clients using replication connections for for example
START_REPLICATION. That would be better than hardcoding a position
like '0/0', and would make the current code more solid.
Patch attached in case.
Regards,
--
Michael
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 34f2fc0..fc42b5f 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -163,7 +163,7 @@ HotStandbyState standbyState = STANDBY_DISABLED;
static XLogRecPtr LastRec;
/* Local copy of WalRcv->receivedUpto */
-static XLogRecPtr receivedUpto = 0;
+static XLogRecPtr receivedUpto = LowestXLogRecPtr;
static TimeLineID receiveTLI = 0;
/*
@@ -11003,7 +11003,7 @@ WaitForWALToBecomeAvailable(XLogRecPtr RecPtr, bool randAccess,
curFileTLI = tli;
RequestXLogStreaming(tli, ptr, PrimaryConnInfo,
PrimarySlotName);
- receivedUpto = 0;
+ receivedUpto = LowestXLogRecPtr;
}
/*
@@ -11266,7 +11266,7 @@ WaitForWALToBecomeAvailable(XLogRecPtr RecPtr, bool randAccess,
static int
emode_for_corrupt_record(int emode, XLogRecPtr RecPtr)
{
- static XLogRecPtr lastComplaint = 0;
+ static XLogRecPtr lastComplaint = LowestXLogRecPtr;
if (readSource == XLOG_FROM_PG_XLOG && emode == LOG)
{
diff --git a/src/backend/replication/walreceiver.c b/src/backend/replication/walreceiver.c
index c2d4ed3..c5103f7 100644
--- a/src/backend/replication/walreceiver.c
+++ b/src/backend/replication/walreceiver.c
@@ -1037,8 +1037,8 @@ XLogWalRcvFlush(bool dying)
static void
XLogWalRcvSendReply(bool force, bool requestReply)
{
- static XLogRecPtr writePtr = 0;
- static XLogRecPtr flushPtr = 0;
+ static XLogRecPtr writePtr = InvalidXLogRecPtr;
+ static XLogRecPtr flushPtr = InvalidXLogRecPtr;
XLogRecPtr applyPtr;
static TimestampTz sendTime = 0;
TimestampTz now;
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 844a5de..819ac28 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -140,7 +140,7 @@ static XLogRecPtr sendTimeLineValidUpto = InvalidXLogRecPtr;
* How far have we sent WAL already? This is also advertised in
* MyWalSnd->sentPtr. (Actually, this is the next WAL location to send.)
*/
-static XLogRecPtr sentPtr = 0;
+static XLogRecPtr sentPtr = LowestXLogRecPtr;
/* Buffers for constructing outgoing messages and processing reply messages. */
static StringInfoData output_message;
diff --git a/src/include/access/xlogdefs.h b/src/include/access/xlogdefs.h
index 3b8e738..f7d88b4 100644
--- a/src/include/access/xlogdefs.h
+++ b/src/include/access/xlogdefs.h
@@ -25,9 +25,13 @@ typedef uint64 XLogRecPtr;
* WAL segment, initializing the first WAL page at XLOG_SEG_SIZE, so no XLOG
* record can begin at zero.
*/
-#define InvalidXLogRecPtr 0
+#define InvalidXLogRecPtr ((XLogRecPtr) 0)
#define XLogRecPtrIsInvalid(r) ((r) == InvalidXLogRecPtr)
+/* Minimum value possible for a location pointer of XLOG */
+#define LowestXLogRecPtr ((XLogRecPtr) 0)
+#define XLogRecPtrIsLowest(r) ((r) == LowestXLogRecPtr)
+
/*
* XLogSegNo - physical log file sequence number.
*/
--
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