a16e00b7b9
Summary: This is implemented by extending ReadCallback with another function `MaxUnpreparedSequenceNumber` which returns the largest visible sequence number for the current transaction, if there is uncommitted data written to DB. Otherwise, it returns zero, indicating no uncommitted data. There are the places where reads had to be modified. - Get and Seek/Next was just updated to seek to max(snapshot_seq, MaxUnpreparedSequenceNumber()) instead, and iterate until a key was visible. - Prev did not need need updates since it did not use the Seek to sequence number optimization. Assuming that locks were held when writing unprepared keys, and ValidateSnapshot runs, there should only be committed keys and unprepared keys of the current transaction, all of which are visible. Prev will simply iterate to get the last visible key. - Reseeking to skip keys optimization was also disabled for write unprepared, since it's possible to hit the max_skip condition even while reseeking. There needs to be some way to resolve infinite looping in this case. Closes https://github.com/facebook/rocksdb/pull/3955 Differential Revision: D8286688 Pulled By: lth fbshipit-source-id: 25e42f47fdeb5f7accea0f4fd350ef35198caafe
31 lines
1.0 KiB
C++
31 lines
1.0 KiB
C++
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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#pragma once
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#include "rocksdb/types.h"
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namespace rocksdb {
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class ReadCallback {
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public:
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virtual ~ReadCallback() {}
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// Will be called to see if the seq number visible; if not it moves on to
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// the next seq number.
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virtual bool IsVisible(SequenceNumber seq) = 0;
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// This is called to determine the maximum visible sequence number for the
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// current transaction for read-your-own-write semantics. This is so that
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// for write unprepared, we will not skip keys that are written by the
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// current transaction with the seek to snapshot optimization.
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//
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// For other uses, this returns zero, meaning that the current snapshot
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// sequence number is the maximum visible sequence number.
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inline virtual SequenceNumber MaxUnpreparedSequenceNumber() { return 0; };
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};
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} // namespace rocksdb
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