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Hot Standby feedback for avoidance of cleanup conflicts on standby.

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Standby optionally sends back information about oldestXmin of queries
which is then checked and applied to the WALSender's proc->xmin.
GetOldestXmin() is modified slightly to agree with GetSnapshotData(),
so that all backends on primary include WALSender within their snapshots.
Note this does nothing to change the snapshot xmin on either master or
standby. Feedback piggybacks on the standby reply message.
vacuum_defer_cleanup_age is no longer used on standby, though parameter
still exists on primary, since some use cases still exist.

Simon Riggs, review comments from Fujii Masao, Heikki Linnakangas, Robert Haas
This commit is contained in:
Simon Riggs
2011-02-16 19:29:37 +00:00
parent 65076269ea
commit bca8b7f16a
11 changed files with 245 additions and 50 deletions
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71
src/backend/replication/walsender.c
View File

@@ -53,6 +53,7 @@
#include "storage/ipc.h"
#include "storage/pmsignal.h"
#include "storage/proc.h"
#include "storage/procarray.h"
#include "tcop/tcopprot.h"
#include "utils/builtins.h"
#include "utils/guc.h"
@@ -502,6 +503,7 @@ ProcessStandbyReplyMessage(void)
{
StandbyReplyMessage reply;
char msgtype;
TransactionId newxmin = InvalidTransactionId;
resetStringInfo(&reply_message);
@@ -531,10 +533,12 @@ ProcessStandbyReplyMessage(void)
pq_copymsgbytes(&reply_message, (char *) &reply, sizeof(StandbyReplyMessage));
elog(DEBUG2, "write %X/%X flush %X/%X apply %X/%X ",
elog(DEBUG2, "write %X/%X flush %X/%X apply %X/%X xmin %u epoch %u",
reply.write.xlogid, reply.write.xrecoff,
reply.flush.xlogid, reply.flush.xrecoff,
reply.apply.xlogid, reply.apply.xrecoff);
reply.apply.xlogid, reply.apply.xrecoff,
reply.xmin,
reply.epoch);
/*
* Update shared state for this WalSender process
@@ -550,6 +554,69 @@ ProcessStandbyReplyMessage(void)
walsnd->apply = reply.apply;
SpinLockRelease(&walsnd->mutex);
}
/*
* Update the WalSender's proc xmin to allow it to be visible
* to snapshots. This will hold back the removal of dead rows
* and thereby prevent the generation of cleanup conflicts
* on the standby server.
*/
if (TransactionIdIsValid(reply.xmin))
{
TransactionId nextXid;
uint32 nextEpoch;
bool epochOK;
GetNextXidAndEpoch(&nextXid, &nextEpoch);
/*
* Epoch of oldestXmin should be same as standby or
* if the counter has wrapped, then one less than reply.
*/
if (reply.xmin <= nextXid)
{
if (reply.epoch == nextEpoch)
epochOK = true;
}
else
{
if (nextEpoch > 0 && reply.epoch == nextEpoch - 1)
epochOK = true;
}
/*
* Feedback from standby must not go backwards, nor should it go
* forwards further than our most recent xid.
*/
if (epochOK && TransactionIdPrecedesOrEquals(reply.xmin, nextXid))
{
if (!TransactionIdIsValid(MyProc->xmin))
{
TransactionId oldestXmin = GetOldestXmin(true, true);
if (TransactionIdPrecedes(oldestXmin, reply.xmin))
newxmin = reply.xmin;
else
newxmin = oldestXmin;
}
else
{
if (TransactionIdPrecedes(MyProc->xmin, reply.xmin))
newxmin = reply.xmin;
else
newxmin = MyProc->xmin; /* stay the same */
}
}
}
/*
* Grab the ProcArrayLock to set xmin, or invalidate for bad reply
*/
if (MyProc->xmin != newxmin)
{
LWLockAcquire(ProcArrayLock, LW_SHARED);
MyProc->xmin = newxmin;
LWLockRelease(ProcArrayLock);
}
}
/* Main loop of walsender process */