mirror of https://github.com/facebook/rocksdb.git
233 lines
7.8 KiB
C++
233 lines
7.8 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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#include "table/block_based/block_prefix_index.h"
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#include <vector>
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#include "memory/arena.h"
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#include "rocksdb/comparator.h"
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#include "rocksdb/slice.h"
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#include "rocksdb/slice_transform.h"
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#include "util/coding.h"
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#include "util/hash.h"
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namespace ROCKSDB_NAMESPACE {
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inline uint32_t Hash(const Slice& s) {
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return ROCKSDB_NAMESPACE::Hash(s.data(), s.size(), 0);
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}
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inline uint32_t PrefixToBucket(const Slice& prefix, uint32_t num_buckets) {
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return Hash(prefix) % num_buckets;
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}
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// The prefix block index is simply a bucket array, with each entry pointing to
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// the blocks that span the prefixes hashed to this bucket.
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//
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// To reduce memory footprint, if there is only one block per bucket, the entry
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// stores the block id directly. If there are more than one blocks per bucket,
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// because of hash collision or a single prefix spanning multiple blocks,
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// the entry points to an array of block ids. The block array is an array of
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// uint32_t's. The first uint32_t indicates the total number of blocks, followed
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// by the block ids.
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//
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// To differentiate the two cases, the high order bit of the entry indicates
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// whether it is a 'pointer' into a separate block array.
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// 0x7FFFFFFF is reserved for empty bucket.
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const uint32_t kNoneBlock = 0x7FFFFFFF;
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const uint32_t kBlockArrayMask = 0x80000000;
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inline bool IsNone(uint32_t block_id) { return block_id == kNoneBlock; }
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inline bool IsBlockId(uint32_t block_id) {
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return (block_id & kBlockArrayMask) == 0;
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}
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inline uint32_t DecodeIndex(uint32_t block_id) {
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uint32_t index = block_id ^ kBlockArrayMask;
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assert(index < kBlockArrayMask);
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return index;
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}
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inline uint32_t EncodeIndex(uint32_t index) {
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assert(index < kBlockArrayMask);
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return index | kBlockArrayMask;
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}
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// temporary storage for prefix information during index building
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struct PrefixRecord {
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Slice prefix;
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uint32_t start_block;
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uint32_t end_block;
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uint32_t num_blocks;
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PrefixRecord* next;
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};
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class BlockPrefixIndex::Builder {
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public:
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explicit Builder(const SliceTransform* internal_prefix_extractor)
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: internal_prefix_extractor_(internal_prefix_extractor) {}
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void Add(const Slice& key_prefix, uint32_t start_block, uint32_t num_blocks) {
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PrefixRecord* record = reinterpret_cast<PrefixRecord*>(
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arena_.AllocateAligned(sizeof(PrefixRecord)));
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record->prefix = key_prefix;
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record->start_block = start_block;
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record->end_block = start_block + num_blocks - 1;
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record->num_blocks = num_blocks;
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prefixes_.push_back(record);
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}
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BlockPrefixIndex* Finish() {
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// For now, use roughly 1:1 prefix to bucket ratio.
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uint32_t num_buckets = static_cast<uint32_t>(prefixes_.size()) + 1;
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// Collect prefix records that hash to the same bucket, into a single
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// linklist.
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std::vector<PrefixRecord*> prefixes_per_bucket(num_buckets, nullptr);
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std::vector<uint32_t> num_blocks_per_bucket(num_buckets, 0);
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for (PrefixRecord* current : prefixes_) {
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uint32_t bucket = PrefixToBucket(current->prefix, num_buckets);
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// merge the prefix block span if the first block of this prefix is
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// connected to the last block of the previous prefix.
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PrefixRecord* prev = prefixes_per_bucket[bucket];
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if (prev) {
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assert(current->start_block >= prev->end_block);
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auto distance = current->start_block - prev->end_block;
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if (distance <= 1) {
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prev->end_block = current->end_block;
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prev->num_blocks = prev->end_block - prev->start_block + 1;
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num_blocks_per_bucket[bucket] += (current->num_blocks + distance - 1);
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continue;
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}
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}
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current->next = prev;
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prefixes_per_bucket[bucket] = current;
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num_blocks_per_bucket[bucket] += current->num_blocks;
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}
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// Calculate the block array buffer size
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uint32_t total_block_array_entries = 0;
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for (uint32_t i = 0; i < num_buckets; i++) {
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uint32_t num_blocks = num_blocks_per_bucket[i];
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if (num_blocks > 1) {
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total_block_array_entries += (num_blocks + 1);
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}
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}
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// Populate the final prefix block index
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uint32_t* block_array_buffer = new uint32_t[total_block_array_entries];
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uint32_t* buckets = new uint32_t[num_buckets];
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uint32_t offset = 0;
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for (uint32_t i = 0; i < num_buckets; i++) {
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uint32_t num_blocks = num_blocks_per_bucket[i];
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if (num_blocks == 0) {
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assert(prefixes_per_bucket[i] == nullptr);
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buckets[i] = kNoneBlock;
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} else if (num_blocks == 1) {
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assert(prefixes_per_bucket[i] != nullptr);
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assert(prefixes_per_bucket[i]->next == nullptr);
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buckets[i] = prefixes_per_bucket[i]->start_block;
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} else {
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assert(total_block_array_entries > 0);
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assert(prefixes_per_bucket[i] != nullptr);
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buckets[i] = EncodeIndex(offset);
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block_array_buffer[offset] = num_blocks;
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uint32_t* last_block = &block_array_buffer[offset + num_blocks];
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auto current = prefixes_per_bucket[i];
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// populate block ids from largest to smallest
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while (current != nullptr) {
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for (uint32_t iter = 0; iter < current->num_blocks; iter++) {
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*last_block = current->end_block - iter;
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last_block--;
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}
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current = current->next;
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}
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assert(last_block == &block_array_buffer[offset]);
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offset += (num_blocks + 1);
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}
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}
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assert(offset == total_block_array_entries);
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return new BlockPrefixIndex(internal_prefix_extractor_, num_buckets,
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buckets, total_block_array_entries,
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block_array_buffer);
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}
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private:
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const SliceTransform* internal_prefix_extractor_;
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std::vector<PrefixRecord*> prefixes_;
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Arena arena_;
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};
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Status BlockPrefixIndex::Create(const SliceTransform* internal_prefix_extractor,
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const Slice& prefixes, const Slice& prefix_meta,
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BlockPrefixIndex** prefix_index) {
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uint64_t pos = 0;
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auto meta_pos = prefix_meta;
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Status s;
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Builder builder(internal_prefix_extractor);
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while (!meta_pos.empty()) {
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uint32_t prefix_size = 0;
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uint32_t entry_index = 0;
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uint32_t num_blocks = 0;
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if (!GetVarint32(&meta_pos, &prefix_size) ||
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!GetVarint32(&meta_pos, &entry_index) ||
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!GetVarint32(&meta_pos, &num_blocks)) {
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s = Status::Corruption(
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"Corrupted prefix meta block: unable to read from it.");
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break;
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}
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if (pos + prefix_size > prefixes.size()) {
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s = Status::Corruption(
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"Corrupted prefix meta block: size inconsistency.");
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break;
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}
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Slice prefix(prefixes.data() + pos, prefix_size);
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builder.Add(prefix, entry_index, num_blocks);
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pos += prefix_size;
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}
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if (s.ok() && pos != prefixes.size()) {
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s = Status::Corruption("Corrupted prefix meta block");
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}
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if (s.ok()) {
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*prefix_index = builder.Finish();
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}
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return s;
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}
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uint32_t BlockPrefixIndex::GetBlocks(const Slice& key, uint32_t** blocks) {
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Slice prefix = internal_prefix_extractor_->Transform(key);
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uint32_t bucket = PrefixToBucket(prefix, num_buckets_);
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uint32_t block_id = buckets_[bucket];
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if (IsNone(block_id)) {
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return 0;
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} else if (IsBlockId(block_id)) {
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*blocks = &buckets_[bucket];
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return 1;
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} else {
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uint32_t index = DecodeIndex(block_id);
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assert(index < num_block_array_buffer_entries_);
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*blocks = &block_array_buffer_[index + 1];
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uint32_t num_blocks = block_array_buffer_[index];
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assert(num_blocks > 1);
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assert(index + num_blocks < num_block_array_buffer_entries_);
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return num_blocks;
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}
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}
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} // namespace ROCKSDB_NAMESPACE
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