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fix(wal iterator): Optimized the illusion of triggering "TryAgain" [issue 9948] #9949

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fix(wal iterator): Optimized the illusion of triggering "TryAgain" [issue 9948] #9949

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14 changes: 12 additions & 2 deletions db/transaction_log_impl.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -93,6 +93,15 @@ bool TransactionLogIteratorImpl::RestrictedRead(Slice* record) {
return current_log_reader_->ReadRecord(record, &scratch_);
}

bool TransactionLogIteratorImpl::RestrictedRead(Slice* record, SequenceNumber *sn) {
// Don't read if no more complete entries to read from logs
*sn = versions_->LastSequence();
if (current_last_seq_ >= *sn) {
return false;
}
return current_log_reader_->ReadRecord(record, &scratch_);
}

void TransactionLogIteratorImpl::SeekToStartSequence(uint64_t start_file_index,
bool strict) {
Slice record;
Expand Down Expand Up @@ -181,12 +190,13 @@ void TransactionLogIteratorImpl::NextImpl(bool internal) {
// Runs every time until we can seek to the start sequence
SeekToStartSequence();
}
SequenceNumber sn;
while(true) {
assert(current_log_reader_);
if (current_log_reader_->IsEOF()) {
current_log_reader_->UnmarkEOF();
}
while (RestrictedRead(&record)) {
while (RestrictedRead(&record, &sn)) {
if (record.size() < WriteBatchInternal::kHeader) {
reporter_.Corruption(
record.size(), Status::Corruption("very small log record"));
Expand Down Expand Up @@ -215,7 +225,7 @@ void TransactionLogIteratorImpl::NextImpl(bool internal) {
}
} else {
is_valid_ = false;
if (current_last_seq_ == versions_->LastSequence()) {
if (current_last_seq_ == sn) {
current_status_ = Status::OK();
} else {
const char* msg = "Create a new iterator to fetch the new tail.";
Expand Down
1 change: 1 addition & 0 deletions db/transaction_log_impl.h
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Original file line number Diff line number Diff line change
Expand Up @@ -113,6 +113,7 @@ class TransactionLogIteratorImpl : public TransactionLogIterator {
SequenceNumber current_last_seq_; // last sequence in the current batch
// Reads from transaction log only if the writebatch record has been written
bool RestrictedRead(Slice* record);
bool RestrictedRead(Slice* record, SequenceNumber* last_seq);
// Seeks to starting_sequence_number_ reading from start_file_index in files_.
// If strict is set, then must get a batch starting with
// starting_sequence_number_.
Expand Down