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Fix data duplication in zero copy replication

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This commit is contained in:
alesapin 2022-09-15 18:54:27 +02:00
parent fac1bf224e
commit b098c1be36
3 changed files with 49 additions and 1 deletions
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21
src/Storages/MergeTree/MergeFromLogEntryTask.cpp
View File

@ -223,6 +223,27 @@ ReplicatedMergeMutateTaskBase::PrepareResult MergeFromLogEntryTask::prepare()
.part_log_writer = {}
};
}
else if (!storage.findReplicaHavingCoveringPart(entry.new_part_name, true, dummy).empty())
{
/// Why this if still needed? We can check for part in zookeeper, don't find it and sleep for any amount of time. During this sleep part will be actually commited from other replica
/// and exclusive zero copy lock will be released. We will take the lock and execute merge one more time, while it was possible just to download the part from other replica.
///
/// It's also posible just because reads in [Zoo]Keeper are not lineariazable.
///
/// NOTE: In case of mutation and hardlinks it can even lead to extremely rare dataloss (we will produce new part with the same hardlinks, don't fetch the same from other replica), so this check is important.
zero_copy_lock->lock->unlock();
LOG_DEBUG(log, "We took zero copy lock, but merge of part {} finished by some other replica, will release lock and download merged part to avoid data duplication", entry.new_part_name);
return PrepareResult{
.prepared_successfully = false,
.need_to_check_missing_part_in_fetch = true,
.part_log_writer = {}
};
}
else
{
LOG_DEBUG(log, "Zero copy lock taken, will merge part {}", entry.new_part_name);
}
}
}

21
src/Storages/MergeTree/MutateFromLogEntryTask.cpp
View File

@ -134,6 +134,27 @@ ReplicatedMergeMutateTaskBase::PrepareResult MutateFromLogEntryTask::prepare()
.part_log_writer = {}
};
}
else if (!storage.findReplicaHavingCoveringPart(entry.new_part_name, true, dummy).empty())
{
/// Why this if still needed? We can check for part in zookeeper, don't find it and sleep for any amount of time. During this sleep part will be actually commited from other replica
/// and exclusive zero copy lock will be released. We will take the lock and execute mutation one more time, while it was possible just to download the part from other replica.
///
/// It's also posible just because reads in [Zoo]Keeper are not lineariazable.
///
/// NOTE: In case of mutation and hardlinks it can even lead to extremely rare dataloss (we will produce new part with the same hardlinks, don't fetch the same from other replica), so this check is important.
zero_copy_lock->lock->unlock();
LOG_DEBUG(log, "We took zero copy lock, but mutation of part {} finished by some other replica, will release lock and download mutated part to avoid data duplication", entry.new_part_name);
return PrepareResult{
.prepared_successfully = false,
.need_to_check_missing_part_in_fetch = true,
.part_log_writer = {}
};
}
else
{
LOG_DEBUG(log, "Zero copy lock taken, will mutate part {}", entry.new_part_name);
}
}
}

8
src/Storages/MergeTree/MutateFromLogEntryTask.h
View File

@ -6,6 +6,7 @@
#include <Storages/MergeTree/ReplicatedMergeTreeQueue.h>
#include <Storages/MergeTree/ReplicatedMergeTreeLogEntry.h>
#include <Storages/MergeTree/ZeroCopyLock.h>
#include <Storages/StorageReplicatedMergeTree.h>
namespace DB
{
@ -18,7 +19,12 @@ public:
ReplicatedMergeTreeQueue::SelectedEntryPtr selected_entry_,
StorageReplicatedMergeTree & storage_,
Callback && task_result_callback_)
: ReplicatedMergeMutateTaskBase(&Poco::Logger::get("MutateFromLogEntryTask"), storage_, selected_entry_, task_result_callback_) {}
: ReplicatedMergeMutateTaskBase(
&Poco::Logger::get(storage_.getStorageID().getShortName() + "::" + selected_entry_->log_entry->new_part_name + "(MutateFromLogEntryTask)"),
storage_,
selected_entry_,
task_result_callback_)
{}
UInt64 getPriority() override { return priority; }