Allan Yang created HBASE-17506:
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Summary: started mvcc transaction is not completed in branch-1
Key: HBASE-17506
URL: https://issues.apache.org/jira/browse/HBASE-17506
Project: HBase
Issue Type: Bug
Affects Versions: 1.4.0
Reporter: Allan Yang
Assignee: Allan Yang
In {{doMiniBatchMutation}}, if it is in replay and if the the nonce of the
mutation is different, we append them to a different wal. But, after
HBASE-14465, we start a mvcc transition in the ringbuffer's append thread. So,
every time we append a wal entry, we started a mvcc transition, but we didn't
complete the mvcc transition anywhere. This can block other transition of this
region.
{code}
// txid should always increase, so having the one from the last call is ok.
// we use HLogKey here instead of WALKey directly to support legacy
coprocessors.
walKey = new
ReplayHLogKey(this.getRegionInfo().getEncodedNameAsBytes(),
this.htableDescriptor.getTableName(), now, m.getClusterIds(),
currentNonceGroup, currentNonce, mvcc);
txid = this.wal.append(this.htableDescriptor,
this.getRegionInfo(), walKey,
walEdit, true);
walEdit = new WALEdit(cellCount, isInReplay);
walKey = null;
{code}
Looked at master branch, there is no such problem. It has a method
named{{appendCurrentNonces}} :
{code}
private void appendCurrentNonces(final Mutation mutation, final boolean replay,
final WALEdit walEdit, final long now, final long currentNonceGroup,
final long currentNonce)
throws IOException {
if (walEdit.isEmpty()) return;
if (!replay) throw new IOException("Multiple nonces per batch and not in
replay");
WALKey walKey = new WALKey(this.getRegionInfo().getEncodedNameAsBytes(),
this.htableDescriptor.getTableName(), now, mutation.getClusterIds(),
currentNonceGroup, currentNonce, mvcc, this.getReplicationScope());
this.wal.append(this.getRegionInfo(), walKey, walEdit, true);
// Complete the mvcc transaction started down in append else it will block
others
this.mvcc.complete(walKey.getWriteEntry());
}
{code}
Yes, the easiest way to fix branch-1 is to complete the writeEntry like master
branch do. But is it really fine to do this?
1. Question 1:
complete the mvcc transition before waiting sync will create a disturbance of
data visibility.
2.Question 2:
In what circumstance will there be different nonce and nonce group in a single
wal entry? Nonce are used in append/increment. But in {{batchMuate}} ,we treat
them differently and append one wal entry for each of them. So I think no test
can reach this code path, that maybe why no one has found this bug(Please tell
me if I'm wrong).
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