Krishen Bhan created HUDI-6596:
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Summary: Propose rollback implementation changes to guard against
concurrent jobs
Key: HUDI-6596
URL: https://issues.apache.org/jira/browse/HUDI-6596
Project: Apache Hudi
Issue Type: Wish
Reporter: Krishen Bhan
h1. Issue
The existing rollback API in 0.14
[https://github.com/apache/hudi/blob/master/hudi-client/hudi-client-common/src/main/java/org/apache/hudi/client/BaseHoodieTableServiceClient.java#L877]
executes a rollback plan, either taking in an existing rollback plan provided
by the caller for a previous rollback or attempt, or scheduling a new rollback
instant if none is provided. Currently it is not safe for two concurrent jobs
to call this API (when skipLocking=False and the callers aren't already holding
a lock), as this can lead to an issue where multiple rollback requested plans
are created or two jobs are executing the same rollback instant at the same
time.
h1. Proposed change
One way to resolve this issue is to refactor this rollback function such that
if skipLocking=false, the following steps are followed
# Acquire the table lock
# Reload the active timeline
# Look at the active timeline to see if there is a inflight rollback instant
from a previous rollback attempt, if it exists then assign this is as the
rollback plan to execute. Also, check if a pending rollback plan was passed in
by caller. Then makes the following checks
## [a] If a pending inflight rollback plan was passed in by caller, then
check that there is a previous attempted rollback instant on timeline (and that
the instant times match) and use this rollback plan. If that isn't the case,
then raise a rollback exception since this means another job has concurrently
already executed this plan.
## [b] If no pending inflight rollback plan was passed in by caller, then
schedule a new rollback plan if an existing one wasn't found in active timeline.
# Now that a rollback plan and requested rollback instant time has been
assigned, check for an active heartbeat for the rollback instant time. If there
is one, then abort the rollback as that means there is a concurrent job
executing that rollback. If not, then start a heartbeat for that rollback
instant time.
# Release the table lock
# Execute the rollback plan and complete the rollback instant. Whether this
succeeds or fails with an exception, close the heartbeat. This increases the
chance that the next job that tries to call this rollback API will follow
through with the rollback and not abort due to an active previous heartbeat
* These steps will only be enforced for skipLocking=false, since if
skipLocking=true then that means the caller may already be explicitly holding a
table lock. In this case, acquiring the lock again in step (1) will fail.
* Acquiring a lock and reloading timeline for (1-3) will guard against data
race conditions where another job calls this rollback API at same time and
schedules its own rollback plan and instant. This is since if no rollback has
been attempted before for this instant, then before step (1), there is a window
of time where another concurrent rollback job could have scheduled a rollback
plan, failed execution, and cleaned up heartbeat, all while the current
rollback job is running. As a result, even if the current job was passed in an
empty pending rollback plan, it still needs to check the active timeline to
ensure that no new rollback pending instant has been created.
* Using a heartbeat will signal to other callers in other jobs that there is
another job already executing this rollback. Checking for expired heartbeat and
(re)-starting the heartbeat has to be done under a lock, so that multiple jobs
don't each start it at the same time and assume that they are the only ones
that are heartbeating.
* The table lock is no longer needed after (5), since it can now be safely
assumed that no other job (calling this rollback API) will execute this
rollback instant.
One example implementation to achieve this:
{code:java}
@Deprecated
public boolean rollback(final String commitInstantTime,
Option<HoodiePendingRollbackInfo> pendingRollbackInfo, boolean skipLocking,
Option<String> rollbackInstantTimeOpt) throws HoodieRollbackException {
final Timer.Context timerContext = this.metrics.getRollbackCtx();
final Option<HoodieInstant> commitInstantOpt;
final HoodieTable<T, I, K, O> table;
try {
table = createTable(config, hadoopConf);
} catch (Exception e) {
throw new HoodieRollbackException("Failed to initalize table for rollback "
+ config.getBasePath() + " commits " + commitInstantTime, e);
}
final String rollbackInstantTime;
final boolean deleteInstantsDuringRollback;
final HoodieInstant instantToRollback;
try {
if (!skipLocking) {
// Do step 1 and 2
txnManager.beginTransaction();
table.getMetaClient().reloadActiveTimeline();
}
final Option<HoodiePendingRollbackInfo> previousAttemptedRollback;
if (skipLocking) {
// If skipLocking = true, then there directly use pendingRollbackInfo
without checking the status of this rollback instant on active timeline
// This is since the caller is responsible for ensuring there is no
concurrent rollback
previousAttemptedRollback = pendingRollbackInfo;
} else {
// step 3
// If skipLocking = false, we need to check the timeline for the latest
pending rollback, in case a concurrent rollback before
// step 1 has already executed pendingRollbackInfo
previousAttemptedRollback = getPendingRollbackInfo(table.getMetaClient(),
commitInstantTime, false);
if (pendingRollbackInfo.isPresent()) {
// step 3a If a pendingRollbackInfo was passed in, verify that it is
the same as the pending rollback that was just observed. If not, then
// abort the rollback
previousAttemptedRollback.orElseThrow(
() -> new HoodieRollbackException(
String.format("Pending rollback instant %s no longer inflight",
pendingRollbackInfo.get().getRollbackInstant().getTimestamp())
)
);
// This will only fail if the table is in an illegal state, where there
are 2+ rollback plans for one instant. This
// check shouldn't be necessary, but just keeping it here for now to
demonstrate
ValidationUtils.checkArgument(previousAttemptedRollback.get().getRollbackInstant().getTimestamp().equals(
pendingRollbackInfo.get().getRollbackInstant().getTimestamp())
);
}
}
rollbackInstantTime = previousAttemptedRollback
.map(pendingRollback ->
pendingRollback.getRollbackInstant().getTimestamp())
.orElse(rollbackInstantTimeOpt.orElseGet(() ->
HoodieActiveTimeline.createNewInstantTime()));
commitInstantOpt =
Option.fromJavaOptional(table.getActiveTimeline().getCommitsTimeline().getInstants()
.filter(instant ->
HoodieActiveTimeline.EQUALS.test(instant.getTimestamp(), commitInstantTime))
.findFirst());
LOG.info(String.format("Begin rollback of instant %s at instantTime %s",
commitInstantTime, rollbackInstantTime));
LOG.info(String.format("Scheduling Rollback at instant time : %s "
+ "(exists in active timeline: %s), with rollback plan: %s",
rollbackInstantTime, commitInstantOpt.isPresent(),
previousAttemptedRollback.isPresent()));
if (previousAttemptedRollback.isPresent()) {
if (commitInstantOpt.isPresent()) {
instantToRollback = commitInstantOpt.get();
deleteInstantsDuringRollback = true;
} else {
// A previous pending rollback plan still needs to be executed and
completed even if the instant to rollback
// is no longer in active timeline. This can be safely done by
re-creating the instant to rollback and
// configuring the rollback execution later on to not delete the
instants during rollback.
instantToRollback = new HoodieInstant(
true,
previousAttemptedRollback.get().getRollbackPlan().getInstantToRollback().getAction(),
commitInstantTime);
deleteInstantsDuringRollback = false;
}
} else {
// Step 3b
// A new rollback can only be scheduled if the commit to rollback is
still in the active timeline
if (!commitInstantOpt.isPresent()) {
LOG.warn("Cannot find instant " + commitInstantTime + " in the
timeline, for rollback");
return false;
}
instantToRollback = commitInstantOpt.get();
deleteInstantsDuringRollback = true;
Option<HoodieRollbackPlan> newRollbackPlanOption =
table.scheduleRollback(context, rollbackInstantTime,
commitInstantOpt.get(), false, config.shouldRollbackUsingMarkers());
newRollbackPlanOption.orElseThrow(() -> new HoodieRollbackException(
String.format("Failed to schedule rollback of %s at instant time %s",
commitInstantTime, rollbackInstantTime))
);
}
// Step 4
// This heartbeating logic should/will only be triggered if skipLocking =
false. If
// the rollback instant time has just been newly scheduled these heartbeat
checks will still correctly
// show the (non-existent) heartbeat as expired
if (!skipLocking) {
try {
if (heartbeatClient.isHeartbeatExpired(rollbackInstantTime)) {
heartbeatClient.stop(rollbackInstantTime);
} else {
throw new HoodieRollbackException(String.format("Cannot execute
rollback instant %s due to active heartbeat", rollbackInstantTime);
}
heartbeatClient.start(rollbackInstantTime);
} catch (IOException e) {
throw new HoodieRollbackException(String.format("Could not access last
heartbeat for %s", rollbackInstantTime);
}
}
} catch (Exception e) {
throw new HoodieRollbackException("Failed to use/create rollback plan for"
+ config.getBasePath() + " commits " + commitInstantTime, e);
} finally {
// Step 5
if (!skipLocking) {
txnManager.endTransaction();
}
}
// Step 6
try {
HoodieRollbackMetadata rollbackMetadata = table.rollback(context,
rollbackInstantTime, instantToRollback, deleteInstantsDuringRollback,
skipLocking);
if (timerContext != null) {
long durationInMs = metrics.getDurationInMs(timerContext.stop());
metrics.updateRollbackMetrics(durationInMs,
rollbackMetadata.getTotalFilesDeleted());
}
return true;
} catch (Exception e) {
throw new HoodieRollbackException("Failed to execute rollback " +
config.getBasePath() + " commits " + commitInstantTime, e);
} finally {
if (!skipLocking) {
heartbeatClient.stop(rollbackInstantTime);
}
}
}{code}
h2. Why might this change be useful?
Although these scenarios can be resolved at the application/orchestration level
rather than HUDI, we are still working on this fix in our internal deployment
of HUDI since we want to avoid edge cases where 2+ jobs can call this rollback
API for the same instant at the same time.
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