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Explain waitForVersion why wait for version minus MAX_READ_TRANSACTION_LIFE_VERSIONS

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This commit is contained in:
Meng Xu 2020-11-13 22:14:01 -08:00
parent 222da17558
commit 4b0fba6ea8
1 changed files with 3 additions and 1 deletions
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4
fdbserver/LogRouter.actor.cpp
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@ -245,7 +245,9 @@ ACTOR Future<Void> waitForVersion( LogRouterData *self, Version ver ) {
return Void();
}
if(!self->foundEpochEnd) {
// Why it only needs to wait for (ver - SERVER_KNOBS->MAX_READ_TRANSACTION_LIFE_VERSIONS), instead of ver?
// Similar to proxy that does not keep more than MAX_READ_TRANSACTION_LIFE_VERSIONS transactions oustanding;
// Log router does not keep more than MAX_READ_TRANSACTION_LIFE_VERSIONS transactions outstanding because
// remote SS cannot roll back to more than MAX_READ_TRANSACTION_LIFE_VERSIONS ago.
wait(self->minPopped.whenAtLeast(std::min(self->version.get(), ver - SERVER_KNOBS->MAX_READ_TRANSACTION_LIFE_VERSIONS)));
} else {
while(self->minPopped.get() + SERVER_KNOBS->MAX_READ_TRANSACTION_LIFE_VERSIONS < ver) {