f1bf169484
Summary: With Merge returning bool, it can keep failing silently(eg. While faling to fetch timestamp in TTL). We need to detect this through a rocksdb counter which can get bumped whenever Merge returns false. This will also be super-useful for the mcrocksdb-counter service where Merge may fail. Added a counter NUMBER_MERGE_FAILURES and appropriately updated db/merge_helper.cc I felt that it would be better to directly add counter-bumping in Merge as a default function of MergeOperator class but user should not be aware of this, so this approach seems better to me. Test Plan: make all check Reviewers: dnicholas, haobo, dhruba, vamsi CC: leveldb Differential Revision: https://reviews.facebook.net/D12129
99 lines
3.8 KiB
C++
99 lines
3.8 KiB
C++
#ifndef MERGE_HELPER_H
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#define MERGE_HELPER_H
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#include "db/dbformat.h"
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#include "leveldb/slice.h"
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#include "leveldb/statistics.h"
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#include <string>
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#include <deque>
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namespace leveldb {
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class Comparator;
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class Iterator;
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class Logger;
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class MergeOperator;
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class MergeHelper {
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public:
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MergeHelper(const Comparator* user_comparator,
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const MergeOperator* user_merge_operator,
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Logger* logger,
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bool assert_valid_internal_key)
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: user_comparator_(user_comparator),
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user_merge_operator_(user_merge_operator),
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logger_(logger),
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assert_valid_internal_key_(assert_valid_internal_key),
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keys_(),
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operands_(),
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success_(false) {}
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// Merge entries until we hit
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// - a corrupted key
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// - a Put/Delete,
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// - a different user key,
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// - a specific sequence number (snapshot boundary),
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// or - the end of iteration
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// iter: (IN) points to the first merge type entry
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// (OUT) points to the first entry not included in the merge process
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// stop_before: (IN) a sequence number that merge should not cross.
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// 0 means no restriction
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// at_bottom: (IN) true if the iterator covers the bottem level, which means
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// we could reach the start of the history of this user key.
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void MergeUntil(Iterator* iter, SequenceNumber stop_before = 0,
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bool at_bottom = false, shared_ptr<Statistics> stats=nullptr);
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// Query the merge result
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// These are valid until the next MergeUntil call
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// If the merging was successful:
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// - IsSuccess() will be true
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// - key() will have the latest sequence number of the merges.
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// The type will be Put or Merge. See IMPORTANT 1 note, below.
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// - value() will be the result of merging all the operands together
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// - The user should ignore keys() and values().
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//
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// IMPORTANT 1: the key type could change after the MergeUntil call.
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// Put/Delete + Merge + ... + Merge => Put
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// Merge + ... + Merge => Merge
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//
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// If the merge operator is not associative, and if a Put/Delete is not found
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// then the merging will be unsuccessful. In this case:
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// - IsSuccess() will be false
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// - keys() contains the list of internal keys seen in order of iteration.
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// - values() contains the list of values (merges) seen in the same order.
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// values() is parallel to keys() so that the first entry in
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// keys() is the key associated with the first entry in values()
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// and so on. These lists will be the same length.
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// All of these pairs will be merges over the same user key.
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// See IMPORTANT 2 note below.
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// - The user should ignore key() and value().
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//
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// IMPORTANT 2: The entries were traversed in order from BACK to FRONT.
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// So keys().back() was the first key seen by iterator.
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// TODO: Re-style this comment to be like the first one
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bool IsSuccess() { return success_; }
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Slice key() { assert(success_); return Slice(keys_.back()); }
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Slice value() { assert(success_); return Slice(operands_.back()); }
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const std::deque<std::string>& keys() { assert(!success_); return keys_; }
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const std::deque<std::string>& values() {
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assert(!success_); return operands_;
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}
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private:
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const Comparator* user_comparator_;
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const MergeOperator* user_merge_operator_;
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Logger* logger_;
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Iterator* iter_; // in: the internal iterator, positioned at the first merge entry
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bool assert_valid_internal_key_; // enforce no internal key corruption?
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// the scratch area that holds the result of MergeUntil
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// valid up to the next MergeUntil call
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std::deque<std::string> keys_; // Keeps track of the sequence of keys seen
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std::deque<std::string> operands_; // Parallel with keys_; stores the values
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bool success_;
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};
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} // namespace leveldb
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#endif
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