private static CopyModeResult FindCopyModePrivate(
CopyContextParameters sourceParamaters,
CopyContextParameters targetParameters,
long lastRecoveredAtomicRedoOperationLsnAtTarget)
{
// We can perform the check for CASE 1(Shown Below) before finding the shared ProgressVectorEntry.
// However, we do not do that because the shared ProgressVectorEntry method provides additional checks of epoch history
var sharedProgressVectorEntry = FindSharedVector(
sourceParamaters.ProgressVector,
targetParameters.ProgressVector);
// If we detect that the shared progress vector cannot be obtained because of a trimmed progress vector, we decide to do a full copy
if (sharedProgressVectorEntry.FullCopyReason == FullCopyReason.ProgressVectorTrimmed)
{
return(CopyModeResult.CreateFullCopyResult(null, FullCopyReason.ProgressVectorTrimmed));
}
// Validation failed, perform full copy
if (sharedProgressVectorEntry.FullCopyReason == FullCopyReason.ValidationFailed)
{
return(CopyModeResult.CreateFullCopyResult(sharedProgressVectorEntry, FullCopyReason.ValidationFailed));
}
// *******************************************CASE 1 - COPY_NONE***********************************************************
//
// The last entry in the source and the target vectors are same with the same tail.
// This can happen if target goes down and comes back up and the primary made no progress
if (sourceParamaters.ProgressVector.LastProgressVectorEntry == targetParameters.ProgressVector.LastProgressVectorEntry &&
sourceParamaters.LogTailLsn == targetParameters.LogTailLsn)
{
// Note that copy none covers only cases where nothing needs to be copied (including the UpdateEpochLogRecord)
// Hence, service creation scenario is Partial copy, not None.
return(CopyModeResult.CreateCopyNoneResult(sharedProgressVectorEntry));
}
// *******************************************CASE 2a - COPY_FULL - Due to Data Loss******************************************
//
// Check for any dataloss in the source or target log
// If there was data loss, perform full copy
// No full copy with DataLoss reason, if the target is a brand new replica
if (!ProgressVector.IsBrandNewReplica(targetParameters))
{
if (sharedProgressVectorEntry.SourceProgressVectorEntry.Epoch.DataLossNumber != sourceParamaters.ProgressVector.LastProgressVectorEntry.Epoch.DataLossNumber ||
sharedProgressVectorEntry.TargetProgressVectorEntry.Epoch.DataLossNumber != targetParameters.ProgressVector.LastProgressVectorEntry.Epoch.DataLossNumber ||
sourceParamaters.LogHeadEpoch.DataLossNumber > sharedProgressVectorEntry.TargetProgressVectorEntry.Epoch.DataLossNumber ||
targetParameters.LogHeadEpoch.DataLossNumber > sharedProgressVectorEntry.SourceProgressVectorEntry.Epoch.DataLossNumber)
{
return(CopyModeResult.CreateFullCopyResult(sharedProgressVectorEntry, FullCopyReason.DataLoss));
}
}
var sourceStartingLsn = (sharedProgressVectorEntry.SourceIndex == (sourceParamaters.ProgressVector.vectors.Count - 1))
? sourceParamaters.LogTailLsn
: sourceParamaters.ProgressVector.vectors[sharedProgressVectorEntry.SourceIndex + 1].Lsn;
var targetStartingLsn = (sharedProgressVectorEntry.TargetIndex == (targetParameters.ProgressVector.vectors.Count - 1))
? targetParameters.LogTailLsn
: targetParameters.ProgressVector.vectors[sharedProgressVectorEntry.TargetIndex + 1].Lsn;
// *******************************************CASE 2b - COPY_FULL - Due to Insufficient Loss******************************************
//
// Since there was no data loss, check if we can perform partial copy and there are sufficient logs in the source
// and target to do so
if (sourceParamaters.LogHeadLsn > targetParameters.LogTailLsn ||
sourceStartingLsn < sourceParamaters.LogHeadLsn ||
targetParameters.LogHeadLsn > sourceStartingLsn)
{
return(CopyModeResult.CreateFullCopyResult(sharedProgressVectorEntry, FullCopyReason.InsufficientLogs));
}
// *******************************************CASE 3a - FALSE_PROGRESS -Basic Case******************************************
//
// The simple case where target made more progress in an epoch than the primary
// Source = (1,1,0) (1,3,10) (1,4,15) Tail = 16
// Target = (1,1,0) (1,3,10) Tail = 20
if (sourceStartingLsn < targetStartingLsn)
{
return(CopyModeResult.CreateFalseProgressResult(
lastRecoveredAtomicRedoOperationLsnAtTarget,
sharedProgressVectorEntry,
sourceStartingLsn,
targetStartingLsn));
}
// *******************************************CASE 3b - FALSE_PROGRESS -Advanced Case******************************************
//
// The cases where target has made progress in an epoch that the primary has no knowledge of
// Series of crashes could lead to the target having made false progress in an epoch that the primary DOES NOT KNOW about
// Source = (1,1,0) (1,3,10) Tail = 15
// Target = (1,1,0) (1,2,10) Tail = 12
// Source = (1,1,0) (1,3,10) Tail = 15
// Target = (1,1,0) (1,2,10) Tail = 10
// Source = (1,3,10) (1,5,17) Tail = 18
// Target = (1,3,10) (1,4,15) Tail = 17
if (targetStartingLsn != targetParameters.LogTailLsn)
{
sourceStartingLsn = targetStartingLsn;
return(CopyModeResult.CreateFalseProgressResult(
lastRecoveredAtomicRedoOperationLsnAtTarget,
sharedProgressVectorEntry,
sourceStartingLsn,
targetStartingLsn));
}
// *******************************************CASE 4 - Work Around Case to be able to assert******************************************
// RDBUG : 3374739
// Source = (1,1,0) (1,3,10) Tail >= 10
// Target = (1,1,0) (1,2,5) Tail = 5
// Target got UpdateEpoch(e5) at 5, while source got UpdateEpoch(e6) at 10 (without having an entry for e5)
// Source should detect this and do a full build - (We cannot undo false progress since the process at the target until 5 could be true progress and could be checkpointed)
if (sourceParamaters.ProgressVector.vectors[sharedProgressVectorEntry.SourceIndex].Epoch < targetParameters.ProgressVector.LastProgressVectorEntry.Epoch)
{
return(CopyModeResult.CreateFullCopyResult(sharedProgressVectorEntry, FullCopyReason.Other));
}
return(CopyModeResult.CreatePartialCopyResult(sharedProgressVectorEntry, sourceStartingLsn, targetStartingLsn));
}
