1 files changed, 438 insertions, 0 deletions
diff --git a/src/rocksdb/db/range_tombstone_fragmenter.cc b/src/rocksdb/db/range_tombstone_fragmenter.cc
new file mode 100644
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--- /dev/null
+++ b/src/rocksdb/db/range_tombstone_fragmenter.cc
@@ -0,0 +1,438 @@
+//  Copyright (c) 2018-present, Facebook, Inc.  All rights reserved.
+//  This source code is licensed under both the GPLv2 (found in the
+//  COPYING file in the root directory) and Apache 2.0 License
+//  (found in the LICENSE.Apache file in the root directory).
+
+#include "db/range_tombstone_fragmenter.h"
+
+#include <algorithm>
+#include <functional>
+#include <set>
+
+#include <inttypes.h>
+#include <stdio.h>
+
+#include "util/autovector.h"
+#include "util/kv_map.h"
+#include "util/vector_iterator.h"
+
+namespace rocksdb {
+
+FragmentedRangeTombstoneList::FragmentedRangeTombstoneList(
+    std::unique_ptr<InternalIterator> unfragmented_tombstones,
+    const InternalKeyComparator& icmp, bool for_compaction,
+    const std::vector<SequenceNumber>& snapshots) {
+  if (unfragmented_tombstones == nullptr) {
+    return;
+  }
+  bool is_sorted = true;
+  int num_tombstones = 0;
+  InternalKey pinned_last_start_key;
+  Slice last_start_key;
+  for (unfragmented_tombstones->SeekToFirst(); unfragmented_tombstones->Valid();
+       unfragmented_tombstones->Next(), num_tombstones++) {
+    if (num_tombstones > 0 &&
+        icmp.Compare(last_start_key, unfragmented_tombstones->key()) > 0) {
+      is_sorted = false;
+      break;
+    }
+    if (unfragmented_tombstones->IsKeyPinned()) {
+      last_start_key = unfragmented_tombstones->key();
+    } else {
+      pinned_last_start_key.DecodeFrom(unfragmented_tombstones->key());
+      last_start_key = pinned_last_start_key.Encode();
+    }
+  }
+  if (is_sorted) {
+    FragmentTombstones(std::move(unfragmented_tombstones), icmp, for_compaction,
+                       snapshots);
+    return;
+  }
+
+  // Sort the tombstones before fragmenting them.
+  std::vector<std::string> keys, values;
+  keys.reserve(num_tombstones);
+  values.reserve(num_tombstones);
+  for (unfragmented_tombstones->SeekToFirst(); unfragmented_tombstones->Valid();
+       unfragmented_tombstones->Next()) {
+    keys.emplace_back(unfragmented_tombstones->key().data(),
+                      unfragmented_tombstones->key().size());
+    values.emplace_back(unfragmented_tombstones->value().data(),
+                        unfragmented_tombstones->value().size());
+  }
+  // VectorIterator implicitly sorts by key during construction.
+  auto iter = std::unique_ptr<VectorIterator>(
+      new VectorIterator(std::move(keys), std::move(values), &icmp));
+  FragmentTombstones(std::move(iter), icmp, for_compaction, snapshots);
+}
+
+void FragmentedRangeTombstoneList::FragmentTombstones(
+    std::unique_ptr<InternalIterator> unfragmented_tombstones,
+    const InternalKeyComparator& icmp, bool for_compaction,
+    const std::vector<SequenceNumber>& snapshots) {
+  Slice cur_start_key(nullptr, 0);
+  auto cmp = ParsedInternalKeyComparator(&icmp);
+
+  // Stores the end keys and sequence numbers of range tombstones with a start
+  // key less than or equal to cur_start_key. Provides an ordering by end key
+  // for use in flush_current_tombstones.
+  std::set<ParsedInternalKey, ParsedInternalKeyComparator> cur_end_keys(cmp);
+
+  // Given the next start key in unfragmented_tombstones,
+  // flush_current_tombstones writes every tombstone fragment that starts
+  // and ends with a key before next_start_key, and starts with a key greater
+  // than or equal to cur_start_key.
+  auto flush_current_tombstones = [&](const Slice& next_start_key) {
+    auto it = cur_end_keys.begin();
+    bool reached_next_start_key = false;
+    for (; it != cur_end_keys.end() && !reached_next_start_key; ++it) {
+      Slice cur_end_key = it->user_key;
+      if (icmp.user_comparator()->Compare(cur_start_key, cur_end_key) == 0) {
+        // Empty tombstone.
+        continue;
+      }
+      if (icmp.user_comparator()->Compare(next_start_key, cur_end_key) <= 0) {
+        // All of the end keys in [it, cur_end_keys.end()) are after
+        // next_start_key, so the tombstones they represent can be used in
+        // fragments that start with keys greater than or equal to
+        // next_start_key. However, the end keys we already passed will not be
+        // used in any more tombstone fragments.
+        //
+        // Remove the fully fragmented tombstones and stop iteration after a
+        // final round of flushing to preserve the tombstones we can create more
+        // fragments from.
+        reached_next_start_key = true;
+        cur_end_keys.erase(cur_end_keys.begin(), it);
+        cur_end_key = next_start_key;
+      }
+
+      // Flush a range tombstone fragment [cur_start_key, cur_end_key), which
+      // should not overlap with the last-flushed tombstone fragment.
+      assert(tombstones_.empty() ||
+             icmp.user_comparator()->Compare(tombstones_.back().end_key,
+                                             cur_start_key) <= 0);
+
+      // Sort the sequence numbers of the tombstones being fragmented in
+      // descending order, and then flush them in that order.
+      autovector<SequenceNumber> seqnums_to_flush;
+      for (auto flush_it = it; flush_it != cur_end_keys.end(); ++flush_it) {
+        seqnums_to_flush.push_back(flush_it->sequence);
+      }
+      std::sort(seqnums_to_flush.begin(), seqnums_to_flush.end(),
+                std::greater<SequenceNumber>());
+
+      size_t start_idx = tombstone_seqs_.size();
+      size_t end_idx = start_idx + seqnums_to_flush.size();
+
+      if (for_compaction) {
+        // Drop all tombstone seqnums that are not preserved by a snapshot.
+        SequenceNumber next_snapshot = kMaxSequenceNumber;
+        for (auto seq : seqnums_to_flush) {
+          if (seq <= next_snapshot) {
+            // This seqnum is visible by a lower snapshot.
+            tombstone_seqs_.push_back(seq);
+            seq_set_.insert(seq);
+            auto upper_bound_it =
+                std::lower_bound(snapshots.begin(), snapshots.end(), seq);
+            if (upper_bound_it == snapshots.begin()) {
+              // This seqnum is the topmost one visible by the earliest
+              // snapshot. None of the seqnums below it will be visible, so we
+              // can skip them.
+              break;
+            }
+            next_snapshot = *std::prev(upper_bound_it);
+          }
+        }
+        end_idx = tombstone_seqs_.size();
+      } else {
+        // The fragmentation is being done for reads, so preserve all seqnums.
+        tombstone_seqs_.insert(tombstone_seqs_.end(), seqnums_to_flush.begin(),
+                               seqnums_to_flush.end());
+        seq_set_.insert(seqnums_to_flush.begin(), seqnums_to_flush.end());
+      }
+
+      assert(start_idx < end_idx);
+      tombstones_.emplace_back(cur_start_key, cur_end_key, start_idx, end_idx);
+
+      cur_start_key = cur_end_key;
+    }
+    if (!reached_next_start_key) {
+      // There is a gap between the last flushed tombstone fragment and
+      // the next tombstone's start key. Remove all the end keys in
+      // the working set, since we have fully fragmented their corresponding
+      // tombstones.
+      cur_end_keys.clear();
+    }
+    cur_start_key = next_start_key;
+  };
+
+  pinned_iters_mgr_.StartPinning();
+
+  bool no_tombstones = true;
+  for (unfragmented_tombstones->SeekToFirst(); unfragmented_tombstones->Valid();
+       unfragmented_tombstones->Next()) {
+    const Slice& ikey = unfragmented_tombstones->key();
+    Slice tombstone_start_key = ExtractUserKey(ikey);
+    SequenceNumber tombstone_seq = GetInternalKeySeqno(ikey);
+    if (!unfragmented_tombstones->IsKeyPinned()) {
+      pinned_slices_.emplace_back(tombstone_start_key.data(),
+                                  tombstone_start_key.size());
+      tombstone_start_key = pinned_slices_.back();
+    }
+    no_tombstones = false;
+
+    Slice tombstone_end_key = unfragmented_tombstones->value();
+    if (!unfragmented_tombstones->IsValuePinned()) {
+      pinned_slices_.emplace_back(tombstone_end_key.data(),
+                                  tombstone_end_key.size());
+      tombstone_end_key = pinned_slices_.back();
+    }
+    if (!cur_end_keys.empty() && icmp.user_comparator()->Compare(
+                                     cur_start_key, tombstone_start_key) != 0) {
+      // The start key has changed. Flush all tombstones that start before
+      // this new start key.
+      flush_current_tombstones(tombstone_start_key);
+    }
+    cur_start_key = tombstone_start_key;
+
+    cur_end_keys.emplace(tombstone_end_key, tombstone_seq, kTypeRangeDeletion);
+  }
+  if (!cur_end_keys.empty()) {
+    ParsedInternalKey last_end_key = *std::prev(cur_end_keys.end());
+    flush_current_tombstones(last_end_key.user_key);
+  }
+
+  if (!no_tombstones) {
+    pinned_iters_mgr_.PinIterator(unfragmented_tombstones.release(),
+                                  false /* arena */);
+  }
+}
+
+bool FragmentedRangeTombstoneList::ContainsRange(SequenceNumber lower,
+                                                 SequenceNumber upper) const {
+  auto seq_it = seq_set_.lower_bound(lower);
+  return seq_it != seq_set_.end() && *seq_it <= upper;
+}
+
+FragmentedRangeTombstoneIterator::FragmentedRangeTombstoneIterator(
+    const FragmentedRangeTombstoneList* tombstones,
+    const InternalKeyComparator& icmp, SequenceNumber _upper_bound,
+    SequenceNumber _lower_bound)
+    : tombstone_start_cmp_(icmp.user_comparator()),
+      tombstone_end_cmp_(icmp.user_comparator()),
+      icmp_(&icmp),
+      ucmp_(icmp.user_comparator()),
+      tombstones_(tombstones),
+      upper_bound_(_upper_bound),
+      lower_bound_(_lower_bound) {
+  assert(tombstones_ != nullptr);
+  Invalidate();
+}
+
+FragmentedRangeTombstoneIterator::FragmentedRangeTombstoneIterator(
+    const std::shared_ptr<const FragmentedRangeTombstoneList>& tombstones,
+    const InternalKeyComparator& icmp, SequenceNumber _upper_bound,
+    SequenceNumber _lower_bound)
+    : tombstone_start_cmp_(icmp.user_comparator()),
+      tombstone_end_cmp_(icmp.user_comparator()),
+      icmp_(&icmp),
+      ucmp_(icmp.user_comparator()),
+      tombstones_ref_(tombstones),
+      tombstones_(tombstones_ref_.get()),
+      upper_bound_(_upper_bound),
+      lower_bound_(_lower_bound) {
+  assert(tombstones_ != nullptr);
+  Invalidate();
+}
+
+void FragmentedRangeTombstoneIterator::SeekToFirst() {
+  pos_ = tombstones_->begin();
+  seq_pos_ = tombstones_->seq_begin();
+}
+
+void FragmentedRangeTombstoneIterator::SeekToTopFirst() {
+  if (tombstones_->empty()) {
+    Invalidate();
+    return;
+  }
+  pos_ = tombstones_->begin();
+  seq_pos_ = std::lower_bound(tombstones_->seq_iter(pos_->seq_start_idx),
+                              tombstones_->seq_iter(pos_->seq_end_idx),
+                              upper_bound_, std::greater<SequenceNumber>());
+  ScanForwardToVisibleTombstone();
+}
+
+void FragmentedRangeTombstoneIterator::SeekToLast() {
+  pos_ = std::prev(tombstones_->end());
+  seq_pos_ = std::prev(tombstones_->seq_end());
+}
+
+void FragmentedRangeTombstoneIterator::SeekToTopLast() {
+  if (tombstones_->empty()) {
+    Invalidate();
+    return;
+  }
+  pos_ = std::prev(tombstones_->end());
+  seq_pos_ = std::lower_bound(tombstones_->seq_iter(pos_->seq_start_idx),
+                              tombstones_->seq_iter(pos_->seq_end_idx),
+                              upper_bound_, std::greater<SequenceNumber>());
+  ScanBackwardToVisibleTombstone();
+}
+
+void FragmentedRangeTombstoneIterator::Seek(const Slice& target) {
+  if (tombstones_->empty()) {
+    Invalidate();
+    return;
+  }
+  SeekToCoveringTombstone(target);
+  ScanForwardToVisibleTombstone();
+}
+
+void FragmentedRangeTombstoneIterator::SeekForPrev(const Slice& target) {
+  if (tombstones_->empty()) {
+    Invalidate();
+    return;
+  }
+  SeekForPrevToCoveringTombstone(target);
+  ScanBackwardToVisibleTombstone();
+}
+
+void FragmentedRangeTombstoneIterator::SeekToCoveringTombstone(
+    const Slice& target) {
+  pos_ = std::upper_bound(tombstones_->begin(), tombstones_->end(), target,
+                          tombstone_end_cmp_);
+  if (pos_ == tombstones_->end()) {
+    // All tombstones end before target.
+    seq_pos_ = tombstones_->seq_end();
+    return;
+  }
+  seq_pos_ = std::lower_bound(tombstones_->seq_iter(pos_->seq_start_idx),
+                              tombstones_->seq_iter(pos_->seq_end_idx),
+                              upper_bound_, std::greater<SequenceNumber>());
+}
+
+void FragmentedRangeTombstoneIterator::SeekForPrevToCoveringTombstone(
+    const Slice& target) {
+  if (tombstones_->empty()) {
+    Invalidate();
+    return;
+  }
+  pos_ = std::upper_bound(tombstones_->begin(), tombstones_->end(), target,
+                          tombstone_start_cmp_);
+  if (pos_ == tombstones_->begin()) {
+    // All tombstones start after target.
+    Invalidate();
+    return;
+  }
+  --pos_;
+  seq_pos_ = std::lower_bound(tombstones_->seq_iter(pos_->seq_start_idx),
+                              tombstones_->seq_iter(pos_->seq_end_idx),
+                              upper_bound_, std::greater<SequenceNumber>());
+}
+
+void FragmentedRangeTombstoneIterator::ScanForwardToVisibleTombstone() {
+  while (pos_ != tombstones_->end() &&
+         (seq_pos_ == tombstones_->seq_iter(pos_->seq_end_idx) ||
+          *seq_pos_ < lower_bound_)) {
+    ++pos_;
+    if (pos_ == tombstones_->end()) {
+      Invalidate();
+      return;
+    }
+    seq_pos_ = std::lower_bound(tombstones_->seq_iter(pos_->seq_start_idx),
+                                tombstones_->seq_iter(pos_->seq_end_idx),
+                                upper_bound_, std::greater<SequenceNumber>());
+  }
+}
+
+void FragmentedRangeTombstoneIterator::ScanBackwardToVisibleTombstone() {
+  while (pos_ != tombstones_->end() &&
+         (seq_pos_ == tombstones_->seq_iter(pos_->seq_end_idx) ||
+          *seq_pos_ < lower_bound_)) {
+    if (pos_ == tombstones_->begin()) {
+      Invalidate();
+      return;
+    }
+    --pos_;
+    seq_pos_ = std::lower_bound(tombstones_->seq_iter(pos_->seq_start_idx),
+                                tombstones_->seq_iter(pos_->seq_end_idx),
+                                upper_bound_, std::greater<SequenceNumber>());
+  }
+}
+
+void FragmentedRangeTombstoneIterator::Next() {
+  ++seq_pos_;
+  if (seq_pos_ == tombstones_->seq_iter(pos_->seq_end_idx)) {
+    ++pos_;
+  }
+}
+
+void FragmentedRangeTombstoneIterator::TopNext() {
+  ++pos_;
+  if (pos_ == tombstones_->end()) {
+    return;
+  }
+  seq_pos_ = std::lower_bound(tombstones_->seq_iter(pos_->seq_start_idx),
+                              tombstones_->seq_iter(pos_->seq_end_idx),
+                              upper_bound_, std::greater<SequenceNumber>());
+  ScanForwardToVisibleTombstone();
+}
+
+void FragmentedRangeTombstoneIterator::Prev() {
+  if (seq_pos_ == tombstones_->seq_begin()) {
+    Invalidate();
+    return;
+  }
+  --seq_pos_;
+  if (pos_ == tombstones_->end() ||
+      seq_pos_ == tombstones_->seq_iter(pos_->seq_start_idx - 1)) {
+    --pos_;
+  }
+}
+
+void FragmentedRangeTombstoneIterator::TopPrev() {
+  if (pos_ == tombstones_->begin()) {
+    Invalidate();
+    return;
+  }
+  --pos_;
+  seq_pos_ = std::lower_bound(tombstones_->seq_iter(pos_->seq_start_idx),
+                              tombstones_->seq_iter(pos_->seq_end_idx),
+                              upper_bound_, std::greater<SequenceNumber>());
+  ScanBackwardToVisibleTombstone();
+}
+
+bool FragmentedRangeTombstoneIterator::Valid() const {
+  return tombstones_ != nullptr && pos_ != tombstones_->end();
+}
+
+SequenceNumber FragmentedRangeTombstoneIterator::MaxCoveringTombstoneSeqnum(
+    const Slice& user_key) {
+  SeekToCoveringTombstone(user_key);
+  return ValidPos() && ucmp_->Compare(start_key(), user_key) <= 0 ? seq() : 0;
+}
+
+std::map<SequenceNumber, std::unique_ptr<FragmentedRangeTombstoneIterator>>
+FragmentedRangeTombstoneIterator::SplitBySnapshot(
+    const std::vector<SequenceNumber>& snapshots) {
+  std::map<SequenceNumber, std::unique_ptr<FragmentedRangeTombstoneIterator>>
+      splits;
+  SequenceNumber lower = 0;
+  SequenceNumber upper;
+  for (size_t i = 0; i <= snapshots.size(); i++) {
+    if (i >= snapshots.size()) {
+      upper = kMaxSequenceNumber;
+    } else {
+      upper = snapshots[i];
+    }
+    if (tombstones_->ContainsRange(lower, upper)) {
+      splits.emplace(upper, std::unique_ptr<FragmentedRangeTombstoneIterator>(
+                                new FragmentedRangeTombstoneIterator(
+                                    tombstones_, *icmp_, upper, lower)));
+    }
+    lower = upper + 1;
+  }
+  return splits;
+}
+
+}  // namespace rocksdb