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HBASE-10329 Fail the writes rather than proceeding silently to prevent data loss when AsyncSyncer encounters null writer and its writes aren't synced by other Asyncer 

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1557839 13f79535-47bb-0310-9956-ffa450edef68
This commit is contained in:
Zhihong Yu 2014-01-13 20:38:24 +00:00
parent 721147acf5
commit f492b3fc63
1 changed files with 30 additions and 3 deletions
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33
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/wal/FSHLog.java
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@ -1206,11 +1206,36 @@ class FSHLog implements HLog, Syncable {
// 2. do 'sync' to HDFS to provide durability
long now = EnvironmentEdgeManager.currentTimeMillis();
try {
this.isSyncing = true;
if (writer != null) {
writer.sync();
if (writer == null) {
// the only possible case where writer == null is as below:
// 1. t1: AsyncWriter append writes to hdfs,
// envokes AsyncSyncer 1 with writtenTxid==100
// 2. t2: AsyncWriter append writes to hdfs,
// envokes AsyncSyncer 2 with writtenTxid==200
// 3. t3: rollWriter starts, it grabs the updateLock which
// prevents further writes entering pendingWrites and
// wait for all items(200) in pendingWrites to append/sync
// to hdfs
// 4. t4: AsyncSyncer 2 finishes, now syncedTillHere==200
// 5. t5: rollWriter close writer, set writer=null...
// 6. t6: AsyncSyncer 1 starts to use writer to do sync... before
// rollWriter set writer to the newly created Writer
//
// So when writer == null here:
// 1. if txidToSync <= syncedTillHere, can safely ignore sync here;
// 2. if txidToSync > syncedTillHere, we need fail all the writes with
// txid <= txidToSync to avoid 'data loss' where user get successful
// write response but can't read the writes!
if (this.txidToSync > syncedTillHere.get()) {
LOG.fatal("should never happen: has unsynced writes but writer is null!");
asyncIOE = new IOException("has unsynced writes but writer is null!");
failedTxid.set(this.txidToSync);
}
} else {
this.isSyncing = true;
writer.sync();
this.isSyncing = false;
}
postSync();
} catch (IOException e) {
LOG.fatal("Error while AsyncSyncer sync, request close of hlog ", e);
@ -1218,6 +1243,8 @@ class FSHLog implements HLog, Syncable {
asyncIOE = e;
failedTxid.set(this.txidToSync);
this.isSyncing = false;
}
metrics.finishSync(EnvironmentEdgeManager.currentTimeMillis() - now);