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rocksdb/table/block_based/block.cc

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// Copyright (c) 2011-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).
//
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.
//
// Decodes the blocks generated by block_builder.cc.
#include "table/block_based/block.h"
#include <algorithm>
#include <string>
#include <unordered_map>
#include <vector>
#include "monitoring/perf_context_imp.h"
#include "port/port.h"
#include "port/stack_trace.h"
#include "rocksdb/comparator.h"
#include "table/block_based/block_prefix_index.h"
#include "table/block_based/data_block_footer.h"
#include "table/format.h"
#include "util/coding.h"
namespace ROCKSDB_NAMESPACE {
// Helper routine: decode the next block entry starting at "p",
// storing the number of shared key bytes, non_shared key bytes,
// and the length of the value in "*shared", "*non_shared", and
// "*value_length", respectively. Will not derefence past "limit".
//
// If any errors are detected, returns nullptr. Otherwise, returns a
// pointer to the key delta (just past the three decoded values).
struct DecodeEntry {
inline const char* operator()(const char* p, const char* limit,
uint32_t* shared, uint32_t* non_shared,
uint32_t* value_length) {
// We need 2 bytes for shared and non_shared size. We also need one more
// byte either for value size or the actual value in case of value delta
// encoding.
assert(limit - p >= 3);
*shared = reinterpret_cast<const unsigned char*>(p)[0];
*non_shared = reinterpret_cast<const unsigned char*>(p)[1];
*value_length = reinterpret_cast<const unsigned char*>(p)[2];
if ((*shared | *non_shared | *value_length) < 128) {
// Fast path: all three values are encoded in one byte each
p += 3;
} else {
if ((p = GetVarint32Ptr(p, limit, shared)) == nullptr) return nullptr;
if ((p = GetVarint32Ptr(p, limit, non_shared)) == nullptr) return nullptr;
if ((p = GetVarint32Ptr(p, limit, value_length)) == nullptr) {
return nullptr;
}
}
// Using an assert in place of "return null" since we should not pay the
// cost of checking for corruption on every single key decoding
assert(!(static_cast<uint32_t>(limit - p) < (*non_shared + *value_length)));
return p;
}
};
// Helper routine: similar to DecodeEntry but does not have assertions.
// Instead, returns nullptr so that caller can detect and report failure.
struct CheckAndDecodeEntry {
inline const char* operator()(const char* p, const char* limit,
uint32_t* shared, uint32_t* non_shared,
uint32_t* value_length) {
// We need 2 bytes for shared and non_shared size. We also need one more
// byte either for value size or the actual value in case of value delta
// encoding.
if (limit - p < 3) {
return nullptr;
}
*shared = reinterpret_cast<const unsigned char*>(p)[0];
*non_shared = reinterpret_cast<const unsigned char*>(p)[1];
*value_length = reinterpret_cast<const unsigned char*>(p)[2];
if ((*shared | *non_shared | *value_length) < 128) {
// Fast path: all three values are encoded in one byte each
p += 3;
} else {
if ((p = GetVarint32Ptr(p, limit, shared)) == nullptr) return nullptr;
if ((p = GetVarint32Ptr(p, limit, non_shared)) == nullptr) return nullptr;
if ((p = GetVarint32Ptr(p, limit, value_length)) == nullptr) {
return nullptr;
}
}
if (static_cast<uint32_t>(limit - p) < (*non_shared + *value_length)) {
return nullptr;
}
return p;
}
};
struct DecodeKey {
inline const char* operator()(const char* p, const char* limit,
uint32_t* shared, uint32_t* non_shared) {
uint32_t value_length;
return DecodeEntry()(p, limit, shared, non_shared, &value_length);
}
};
// In format_version 4, which is used by index blocks, the value size is not
// encoded before the entry, as the value is known to be the handle with the
// known size.
struct DecodeKeyV4 {
inline const char* operator()(const char* p, const char* limit,
uint32_t* shared, uint32_t* non_shared) {
// We need 2 bytes for shared and non_shared size. We also need one more
// byte either for value size or the actual value in case of value delta
// encoding.
if (limit - p < 3) return nullptr;
*shared = reinterpret_cast<const unsigned char*>(p)[0];
*non_shared = reinterpret_cast<const unsigned char*>(p)[1];
if ((*shared | *non_shared) < 128) {
// Fast path: all three values are encoded in one byte each
p += 2;
} else {
if ((p = GetVarint32Ptr(p, limit, shared)) == nullptr) return nullptr;
if ((p = GetVarint32Ptr(p, limit, non_shared)) == nullptr) return nullptr;
}
return p;
}
};
struct DecodeEntryV4 {
inline const char* operator()(const char* p, const char* limit,
uint32_t* shared, uint32_t* non_shared,
uint32_t* value_length) {
assert(value_length);
*value_length = 0;
return DecodeKeyV4()(p, limit, shared, non_shared);
}
};
void DataBlockIter::NextImpl() {
bool is_shared = false;
ParseNextDataKey(&is_shared);
}
void MetaBlockIter::NextImpl() {
bool is_shared = false;
ParseNextKey<CheckAndDecodeEntry>(&is_shared);
}
void IndexBlockIter::NextImpl() { ParseNextIndexKey(); }
void IndexBlockIter::PrevImpl() {
assert(Valid());
// Scan backwards to a restart point before current_
const uint32_t original = current_;
while (GetRestartPoint(restart_index_) >= original) {
if (restart_index_ == 0) {
// No more entries
current_ = restarts_;
restart_index_ = num_restarts_;
return;
}
restart_index_--;
}
SeekToRestartPoint(restart_index_);
// Loop until end of current entry hits the start of original entry
while (ParseNextIndexKey() && NextEntryOffset() < original) {
}
}
void MetaBlockIter::PrevImpl() {
assert(Valid());
// Scan backwards to a restart point before current_
const uint32_t original = current_;
while (GetRestartPoint(restart_index_) >= original) {
if (restart_index_ == 0) {
// No more entries
current_ = restarts_;
restart_index_ = num_restarts_;
return;
}
restart_index_--;
}
SeekToRestartPoint(restart_index_);
bool is_shared = false;
// Loop until end of current entry hits the start of original entry
while (ParseNextKey<CheckAndDecodeEntry>(&is_shared) &&
NextEntryOffset() < original) {
}
}
// Similar to IndexBlockIter::PrevImpl but also caches the prev entries
void DataBlockIter::PrevImpl() {
assert(Valid());
assert(prev_entries_idx_ == -1 ||
static_cast<size_t>(prev_entries_idx_) < prev_entries_.size());
// Check if we can use cached prev_entries_
if (prev_entries_idx_ > 0 &&
prev_entries_[prev_entries_idx_].offset == current_) {
// Read cached CachedPrevEntry
prev_entries_idx_--;
const CachedPrevEntry& current_prev_entry =
prev_entries_[prev_entries_idx_];
const char* key_ptr = nullptr;
bool raw_key_cached;
if (current_prev_entry.key_ptr != nullptr) {
// The key is not delta encoded and stored in the data block
key_ptr = current_prev_entry.key_ptr;
raw_key_cached = false;
} else {
// The key is delta encoded and stored in prev_entries_keys_buff_
key_ptr = prev_entries_keys_buff_.data() + current_prev_entry.key_offset;
raw_key_cached = true;
}
const Slice current_key(key_ptr, current_prev_entry.key_size);
current_ = current_prev_entry.offset;
// TODO(ajkr): the copy when `raw_key_cached` is done here for convenience,
// not necessity. It is convenient since this class treats keys as pinned
// when `raw_key_` points to an outside buffer. So we cannot allow
// `raw_key_` point into Prev cache as it is a transient outside buffer
// (i.e., keys in it are not actually pinned).
raw_key_.SetKey(current_key, raw_key_cached /* copy */);
value_ = current_prev_entry.value;
return;
}
// Clear prev entries cache
prev_entries_idx_ = -1;
prev_entries_.clear();
prev_entries_keys_buff_.clear();
// Scan backwards to a restart point before current_
const uint32_t original = current_;
while (GetRestartPoint(restart_index_) >= original) {
if (restart_index_ == 0) {
// No more entries
current_ = restarts_;
restart_index_ = num_restarts_;
return;
}
restart_index_--;
}
SeekToRestartPoint(restart_index_);
do {
bool is_shared = false;
if (!ParseNextDataKey(&is_shared)) {
break;
}
Slice current_key = raw_key_.GetKey();
if (raw_key_.IsKeyPinned()) {
// The key is not delta encoded
prev_entries_.emplace_back(current_, current_key.data(), 0,
current_key.size(), value());
} else {
// The key is delta encoded, cache decoded key in buffer
size_t new_key_offset = prev_entries_keys_buff_.size();
prev_entries_keys_buff_.append(current_key.data(), current_key.size());
prev_entries_.emplace_back(current_, nullptr, new_key_offset,
current_key.size(), value());
}
// Loop until end of current entry hits the start of original entry
} while (NextEntryOffset() < original);
prev_entries_idx_ = static_cast<int32_t>(prev_entries_.size()) - 1;
}
void DataBlockIter::SeekImpl(const Slice& target) {
Slice seek_key = target;
PERF_TIMER_GUARD(block_seek_nanos);
if (data_ == nullptr) { // Not init yet
return;
}
uint32_t index = 0;
bool skip_linear_scan = false;
bool ok = BinarySeek<DecodeKey>(seek_key, &index, &skip_linear_scan);
if (!ok) {
return;
}
FindKeyAfterBinarySeek(seek_key, index, skip_linear_scan);
}
void MetaBlockIter::SeekImpl(const Slice& target) {
Slice seek_key = target;
PERF_TIMER_GUARD(block_seek_nanos);
if (data_ == nullptr) { // Not init yet
return;
}
uint32_t index = 0;
bool skip_linear_scan = false;
bool ok = BinarySeek<DecodeKey>(seek_key, &index, &skip_linear_scan);
if (!ok) {
return;
}
FindKeyAfterBinarySeek(seek_key, index, skip_linear_scan);
}
// Optimized Seek for point lookup for an internal key `target`
// target = "seek_user_key @ type | seqno".
//
// For any type other than kTypeValue, kTypeDeletion, kTypeSingleDeletion,
// or kTypeBlobIndex, this function behaves identically as Seek().
//
// For any type in kTypeValue, kTypeDeletion, kTypeSingleDeletion,
// or kTypeBlobIndex:
//
// If the return value is FALSE, iter location is undefined, and it means:
// 1) there is no key in this block falling into the range:
// ["seek_user_key @ type | seqno", "seek_user_key @ kTypeDeletion | 0"],
// inclusive; AND
// 2) the last key of this block has a greater user_key from seek_user_key
//
// If the return value is TRUE, iter location has two possibilies:
// 1) If iter is valid, it is set to a location as if set by BinarySeek. In
// this case, it points to the first key with a larger user_key or a matching
// user_key with a seqno no greater than the seeking seqno.
// 2) If the iter is invalid, it means that either all the user_key is less
// than the seek_user_key, or the block ends with a matching user_key but
// with a smaller [ type | seqno ] (i.e. a larger seqno, or the same seqno
// but larger type).
bool DataBlockIter::SeekForGetImpl(const Slice& target) {
Slice target_user_key = ExtractUserKey(target);
uint32_t map_offset = restarts_ + num_restarts_ * sizeof(uint32_t);
uint8_t entry =
data_block_hash_index_->Lookup(data_, map_offset, target_user_key);
if (entry == kCollision) {
// HashSeek not effective, falling back
SeekImpl(target);
return true;
}
if (entry == kNoEntry) {
// Even if we cannot find the user_key in this block, the result may
// exist in the next block. Consider this example:
//
// Block N: [aab@100, ... , app@120]
// boundary key: axy@50 (we make minimal assumption about a boundary key)
// Block N+1: [axy@10, ... ]
//
// If seek_key = axy@60, the search will starts from Block N.
// Even if the user_key is not found in the hash map, the caller still
// have to continue searching the next block.
//
// In this case, we pretend the key is the the last restart interval.
// The while-loop below will search the last restart interval for the
// key. It will stop at the first key that is larger than the seek_key,
// or to the end of the block if no one is larger.
entry = static_cast<uint8_t>(num_restarts_ - 1);
}
uint32_t restart_index = entry;
// check if the key is in the restart_interval
assert(restart_index < num_restarts_);
SeekToRestartPoint(restart_index);
current_ = GetRestartPoint(restart_index);
uint32_t limit = restarts_;
if (restart_index + 1 < num_restarts_) {
limit = GetRestartPoint(restart_index + 1);
}
while (current_ < limit) {
bool shared;
// Here we only linear seek the target key inside the restart interval.
// If a key does not exist inside a restart interval, we avoid
// further searching the block content across restart interval boundary.
//
// TODO(fwu): check the left and right boundary of the restart interval
// to avoid linear seek a target key that is out of range.
if (!ParseNextDataKey(&shared) || CompareCurrentKey(target) >= 0) {
// we stop at the first potential matching user key.
break;
}
}
if (current_ == restarts_) {
// Search reaches to the end of the block. There are three possibilites:
// 1) there is only one user_key match in the block (otherwise collsion).
// the matching user_key resides in the last restart interval, and it
// is the last key of the restart interval and of the block as well.
// ParseNextKey() skiped it as its [ type | seqno ] is smaller.
//
// 2) The seek_key is not found in the HashIndex Lookup(), i.e. kNoEntry,
// AND all existing user_keys in the restart interval are smaller than
// seek_user_key.
//
// 3) The seek_key is a false positive and happens to be hashed to the
// last restart interval, AND all existing user_keys in the restart
// interval are smaller than seek_user_key.
//
// The result may exist in the next block each case, so we return true.
return true;
}
if (icmp_->user_comparator()->Compare(raw_key_.GetUserKey(),
target_user_key) != 0) {
// the key is not in this block and cannot be at the next block either.
return false;
}
// Here we are conservative and only support a limited set of cases
ValueType value_type = ExtractValueType(raw_key_.GetInternalKey());
if (value_type != ValueType::kTypeValue &&
value_type != ValueType::kTypeDeletion &&
value_type != ValueType::kTypeSingleDeletion &&
value_type != ValueType::kTypeBlobIndex) {
SeekImpl(target);
return true;
}
// Result found, and the iter is correctly set.
return true;
}
void IndexBlockIter::SeekImpl(const Slice& target) {
TEST_SYNC_POINT("IndexBlockIter::Seek:0");
PERF_TIMER_GUARD(block_seek_nanos);
if (data_ == nullptr) { // Not init yet
return;
}
Slice seek_key = target;
if (raw_key_.IsUserKey()) {
seek_key = ExtractUserKey(target);
}
status_ = Status::OK();
uint32_t index = 0;
bool skip_linear_scan = false;
bool ok = false;
if (prefix_index_) {
bool prefix_may_exist = true;
ok = PrefixSeek(target, &index, &prefix_may_exist);
if (!prefix_may_exist) {
// This is to let the caller to distinguish between non-existing prefix,
// and when key is larger than the last key, which both set Valid() to
// false.
current_ = restarts_;
status_ = Status::NotFound();
}
// restart interval must be one when hash search is enabled so the binary
// search simply lands at the right place.
skip_linear_scan = true;
} else if (value_delta_encoded_) {
ok = BinarySeek<DecodeKeyV4>(seek_key, &index, &skip_linear_scan);
} else {
ok = BinarySeek<DecodeKey>(seek_key, &index, &skip_linear_scan);
}
if (!ok) {
return;
}
FindKeyAfterBinarySeek(seek_key, index, skip_linear_scan);
}
void DataBlockIter::SeekForPrevImpl(const Slice& target) {
PERF_TIMER_GUARD(block_seek_nanos);
Slice seek_key = target;
if (data_ == nullptr) { // Not init yet
return;
}
uint32_t index = 0;
bool skip_linear_scan = false;
bool ok = BinarySeek<DecodeKey>(seek_key, &index, &skip_linear_scan);
if (!ok) {
return;
}
FindKeyAfterBinarySeek(seek_key, index, skip_linear_scan);
if (!Valid()) {
SeekToLastImpl();
} else {
while (Valid() && CompareCurrentKey(seek_key) > 0) {
PrevImpl();
}
}
}
void MetaBlockIter::SeekForPrevImpl(const Slice& target) {
PERF_TIMER_GUARD(block_seek_nanos);
Slice seek_key = target;
if (data_ == nullptr) { // Not init yet
return;
}
uint32_t index = 0;
bool skip_linear_scan = false;
bool ok = BinarySeek<DecodeKey>(seek_key, &index, &skip_linear_scan);
if (!ok) {
return;
}
FindKeyAfterBinarySeek(seek_key, index, skip_linear_scan);
if (!Valid()) {
SeekToLastImpl();
} else {
while (Valid() && CompareCurrentKey(seek_key) > 0) {
PrevImpl();
}
}
}
void DataBlockIter::SeekToFirstImpl() {
if (data_ == nullptr) { // Not init yet
return;
}
SeekToRestartPoint(0);
bool is_shared = false;
ParseNextDataKey(&is_shared);
}
void MetaBlockIter::SeekToFirstImpl() {
if (data_ == nullptr) { // Not init yet
return;
}
SeekToRestartPoint(0);
bool is_shared = false;
ParseNextKey<CheckAndDecodeEntry>(&is_shared);
}
void IndexBlockIter::SeekToFirstImpl() {
if (data_ == nullptr) { // Not init yet
return;
}
status_ = Status::OK();
SeekToRestartPoint(0);
ParseNextIndexKey();
}
void DataBlockIter::SeekToLastImpl() {
if (data_ == nullptr) { // Not init yet
return;
}
SeekToRestartPoint(num_restarts_ - 1);
bool is_shared = false;
while (ParseNextDataKey(&is_shared) && NextEntryOffset() < restarts_) {
// Keep skipping
}
}
void MetaBlockIter::SeekToLastImpl() {
if (data_ == nullptr) { // Not init yet
return;
}
SeekToRestartPoint(num_restarts_ - 1);
bool is_shared = false;
while (ParseNextKey<CheckAndDecodeEntry>(&is_shared) &&
NextEntryOffset() < restarts_) {
// Keep skipping
}
}
void IndexBlockIter::SeekToLastImpl() {
if (data_ == nullptr) { // Not init yet
return;
}
status_ = Status::OK();
SeekToRestartPoint(num_restarts_ - 1);
while (ParseNextIndexKey() && NextEntryOffset() < restarts_) {
// Keep skipping
}
}
template <class TValue>
void BlockIter<TValue>::CorruptionError() {
current_ = restarts_;
restart_index_ = num_restarts_;
status_ = Status::Corruption("bad entry in block");
raw_key_.Clear();
value_.clear();
}
template <class TValue>
template <typename DecodeEntryFunc>
bool BlockIter<TValue>::ParseNextKey(bool* is_shared) {
current_ = NextEntryOffset();
const char* p = data_ + current_;
const char* limit = data_ + restarts_; // Restarts come right after data
if (p >= limit) {
// No more entries to return. Mark as invalid.
current_ = restarts_;
restart_index_ = num_restarts_;
return false;
}
// Decode next entry
uint32_t shared, non_shared, value_length;
p = DecodeEntryFunc()(p, limit, &shared, &non_shared, &value_length);
if (p == nullptr || raw_key_.Size() < shared) {
CorruptionError();
return false;
} else {
if (shared == 0) {
*is_shared = false;
// If this key doesn't share any bytes with prev key then we don't need
// to decode it and can use its address in the block directly.
raw_key_.SetKey(Slice(p, non_shared), false /* copy */);
} else {
// This key share `shared` bytes with prev key, we need to decode it
*is_shared = true;
raw_key_.TrimAppend(shared, p, non_shared);
}
value_ = Slice(p + non_shared, value_length);
if (shared == 0) {
while (restart_index_ + 1 < num_restarts_ &&
GetRestartPoint(restart_index_ + 1) < current_) {
++restart_index_;
}
}
// else we are in the middle of a restart interval and the restart_index_
// thus has not changed
return true;
}
}
bool DataBlockIter::ParseNextDataKey(bool* is_shared) {
if (ParseNextKey<DecodeEntry>(is_shared)) {
#ifndef NDEBUG
if (global_seqno_ != kDisableGlobalSequenceNumber) {
// If we are reading a file with a global sequence number we should
// expect that all encoded sequence numbers are zeros and any value
// type is kTypeValue, kTypeMerge, kTypeDeletion,
// kTypeDeletionWithTimestamp, or kTypeRangeDeletion.
uint64_t packed = ExtractInternalKeyFooter(raw_key_.GetKey());
SequenceNumber seqno;
ValueType value_type;
UnPackSequenceAndType(packed, &seqno, &value_type);
assert(value_type == ValueType::kTypeValue ||
value_type == ValueType::kTypeMerge ||
value_type == ValueType::kTypeDeletion ||
value_type == ValueType::kTypeDeletionWithTimestamp ||
value_type == ValueType::kTypeRangeDeletion);
assert(seqno == 0);
}
#endif // NDEBUG
return true;
} else {
return false;
}
}
bool IndexBlockIter::ParseNextIndexKey() {
bool is_shared = false;
bool ok = (value_delta_encoded_) ? ParseNextKey<DecodeEntryV4>(&is_shared)
: ParseNextKey<DecodeEntry>(&is_shared);
if (ok) {
if (value_delta_encoded_ || global_seqno_state_ != nullptr) {
DecodeCurrentValue(is_shared);
}
}
return ok;
}
// The format:
// restart_point 0: k, v (off, sz), k, v (delta-sz), ..., k, v (delta-sz)
// restart_point 1: k, v (off, sz), k, v (delta-sz), ..., k, v (delta-sz)
// ...
// restart_point n-1: k, v (off, sz), k, v (delta-sz), ..., k, v (delta-sz)
// where, k is key, v is value, and its encoding is in parenthesis.
// The format of each key is (shared_size, non_shared_size, shared, non_shared)
// The format of each value, i.e., block handle, is (offset, size) whenever the
// is_shared is false, which included the first entry in each restart point.
// Otherwise the format is delta-size = block handle size - size of last block
// handle.
void IndexBlockIter::DecodeCurrentValue(bool is_shared) {
Slice v(value_.data(), data_ + restarts_ - value_.data());
// Delta encoding is used if `shared` != 0.
Status decode_s __attribute__((__unused__)) = decoded_value_.DecodeFrom(
&v, have_first_key_,
(value_delta_encoded_ && is_shared) ? &decoded_value_.handle : nullptr);
assert(decode_s.ok());
value_ = Slice(value_.data(), v.data() - value_.data());
if (global_seqno_state_ != nullptr) {
// Overwrite sequence number the same way as in DataBlockIter.
IterKey& first_internal_key = global_seqno_state_->first_internal_key;
first_internal_key.SetInternalKey(decoded_value_.first_internal_key,
/* copy */ true);
assert(GetInternalKeySeqno(first_internal_key.GetInternalKey()) == 0);
ValueType value_type = ExtractValueType(first_internal_key.GetKey());
assert(value_type == ValueType::kTypeValue ||
value_type == ValueType::kTypeMerge ||
value_type == ValueType::kTypeDeletion ||
value_type == ValueType::kTypeRangeDeletion);
first_internal_key.UpdateInternalKey(global_seqno_state_->global_seqno,
value_type);
decoded_value_.first_internal_key = first_internal_key.GetKey();
}
}
template <class TValue>
void BlockIter<TValue>::FindKeyAfterBinarySeek(const Slice& target,
uint32_t index,
bool skip_linear_scan) {
// SeekToRestartPoint() only does the lookup in the restart block. We need
// to follow it up with NextImpl() to position the iterator at the restart
// key.
SeekToRestartPoint(index);
NextImpl();
if (!skip_linear_scan) {
// Linear search (within restart block) for first key >= target
uint32_t max_offset;
if (index + 1 < num_restarts_) {
// We are in a non-last restart interval. Since `BinarySeek()` guarantees
// the next restart key is strictly greater than `target`, we can
// terminate upon reaching it without any additional key comparison.
max_offset = GetRestartPoint(index + 1);
} else {
// We are in the last restart interval. The while-loop will terminate by
// `Valid()` returning false upon advancing past the block's last key.
max_offset = std::numeric_limits<uint32_t>::max();
}
while (true) {
NextImpl();
if (!Valid()) {
break;
}
if (current_ == max_offset) {
assert(CompareCurrentKey(target) > 0);
break;
} else if (CompareCurrentKey(target) >= 0) {
break;
}
}
}
}
// Binary searches in restart array to find the starting restart point for the
// linear scan, and stores it in `*index`. Assumes restart array does not
// contain duplicate keys. It is guaranteed that the restart key at `*index + 1`
// is strictly greater than `target` or does not exist (this can be used to
// elide a comparison when linear scan reaches all the way to the next restart
// key). Furthermore, `*skip_linear_scan` is set to indicate whether the
// `*index`th restart key is the final result so that key does not need to be
// compared again later.
template <class TValue>
template <typename DecodeKeyFunc>
bool BlockIter<TValue>::BinarySeek(const Slice& target, uint32_t* index,
bool* skip_linear_scan) {
if (restarts_ == 0) {
// SST files dedicated to range tombstones are written with index blocks
// that have no keys while also having `num_restarts_ == 1`. This would
// cause a problem for `BinarySeek()` as it'd try to access the first key
// which does not exist. We identify such blocks by the offset at which
// their restarts are stored, and return false to prevent any attempted
// key accesses.
return false;
}
*skip_linear_scan = false;
// Loop invariants:
// - Restart key at index `left` is less than or equal to the target key. The
// sentinel index `-1` is considered to have a key that is less than all
// keys.
// - Any restart keys after index `right` are strictly greater than the target
// key.
int64_t left = -1, right = num_restarts_ - 1;
while (left != right) {
// The `mid` is computed by rounding up so it lands in (`left`, `right`].
int64_t mid = left + (right - left + 1) / 2;
uint32_t region_offset = GetRestartPoint(static_cast<uint32_t>(mid));
uint32_t shared, non_shared;
const char* key_ptr = DecodeKeyFunc()(
data_ + region_offset, data_ + restarts_, &shared, &non_shared);
if (key_ptr == nullptr || (shared != 0)) {
CorruptionError();
return false;
}
Slice mid_key(key_ptr, non_shared);
raw_key_.SetKey(mid_key, false /* copy */);
int cmp = CompareCurrentKey(target);
if (cmp < 0) {
// Key at "mid" is smaller than "target". Therefore all
// blocks before "mid" are uninteresting.
left = mid;
} else if (cmp > 0) {
// Key at "mid" is >= "target". Therefore all blocks at or
// after "mid" are uninteresting.
right = mid - 1;
} else {
*skip_linear_scan = true;
left = right = mid;
}
}
if (left == -1) {
// All keys in the block were strictly greater than `target`. So the very
// first key in the block is the final seek result.
*skip_linear_scan = true;
*index = 0;
} else {
*index = static_cast<uint32_t>(left);
}
return true;
}
// Compare target key and the block key of the block of `block_index`.
// Return -1 if error.
int IndexBlockIter::CompareBlockKey(uint32_t block_index, const Slice& target) {
uint32_t region_offset = GetRestartPoint(block_index);
uint32_t shared, non_shared;
const char* key_ptr =
value_delta_encoded_
? DecodeKeyV4()(data_ + region_offset, data_ + restarts_, &shared,
&non_shared)
: DecodeKey()(data_ + region_offset, data_ + restarts_, &shared,
&non_shared);
if (key_ptr == nullptr || (shared != 0)) {
CorruptionError();
return 1; // Return target is smaller
}
Slice block_key(key_ptr, non_shared);
raw_key_.SetKey(block_key, false /* copy */);
return CompareCurrentKey(target);
}
// Binary search in block_ids to find the first block
// with a key >= target
bool IndexBlockIter::BinaryBlockIndexSeek(const Slice& target,
uint32_t* block_ids, uint32_t left,
uint32_t right, uint32_t* index,
bool* prefix_may_exist) {
assert(left <= right);
assert(index);
assert(prefix_may_exist);
*prefix_may_exist = true;
uint32_t left_bound = left;
while (left <= right) {
uint32_t mid = (right + left) / 2;
int cmp = CompareBlockKey(block_ids[mid], target);
if (!status_.ok()) {
return false;
}
if (cmp < 0) {
// Key at "target" is larger than "mid". Therefore all
// blocks before or at "mid" are uninteresting.
left = mid + 1;
} else {
// Key at "target" is <= "mid". Therefore all blocks
// after "mid" are uninteresting.
// If there is only one block left, we found it.
if (left == right) break;
right = mid;
}
}
if (left == right) {
// In one of the two following cases:
// (1) left is the first one of block_ids
// (2) there is a gap of blocks between block of `left` and `left-1`.
// we can further distinguish the case of key in the block or key not
// existing, by comparing the target key and the key of the previous
// block to the left of the block found.
if (block_ids[left] > 0 &&
(left == left_bound || block_ids[left - 1] != block_ids[left] - 1) &&
CompareBlockKey(block_ids[left] - 1, target) > 0) {
current_ = restarts_;
*prefix_may_exist = false;
return false;
}
*index = block_ids[left];
return true;
} else {
assert(left > right);
// If the next block key is larger than seek key, it is possible that
// no key shares the prefix with `target`, or all keys with the same
// prefix as `target` are smaller than prefix. In the latter case,
// we are mandated to set the position the same as the total order.
// In the latter case, either:
// (1) `target` falls into the range of the next block. In this case,
// we can place the iterator to the next block, or
// (2) `target` is larger than all block keys. In this case we can
// keep the iterator invalidate without setting `prefix_may_exist`
// to false.
// We might sometimes end up with setting the total order position
// while there is no key sharing the prefix as `target`, but it
// still follows the contract.
uint32_t right_index = block_ids[right];
assert(right_index + 1 <= num_restarts_);
if (right_index + 1 < num_restarts_) {
if (CompareBlockKey(right_index + 1, target) >= 0) {
*index = right_index + 1;
return true;
} else {
// We have to set the flag here because we are not positioning
// the iterator to the total order position.
*prefix_may_exist = false;
}
}
// Mark iterator invalid
current_ = restarts_;
return false;
}
}
bool IndexBlockIter::PrefixSeek(const Slice& target, uint32_t* index,
bool* prefix_may_exist) {
assert(index);
assert(prefix_may_exist);
assert(prefix_index_);
*prefix_may_exist = true;
Slice seek_key = target;
if (raw_key_.IsUserKey()) {
seek_key = ExtractUserKey(target);
}
uint32_t* block_ids = nullptr;
uint32_t num_blocks = prefix_index_->GetBlocks(target, &block_ids);
if (num_blocks == 0) {
current_ = restarts_;
*prefix_may_exist = false;
return false;
} else {
assert(block_ids);
return BinaryBlockIndexSeek(seek_key, block_ids, 0, num_blocks - 1, index,
prefix_may_exist);
}
}
uint32_t Block::NumRestarts() const {
assert(size_ >= 2 * sizeof(uint32_t));
uint32_t block_footer = DecodeFixed32(data_ + size_ - sizeof(uint32_t));
uint32_t num_restarts = block_footer;
if (size_ > kMaxBlockSizeSupportedByHashIndex) {
// In BlockBuilder, we have ensured a block with HashIndex is less than
// kMaxBlockSizeSupportedByHashIndex (64KiB).
//
// Therefore, if we encounter a block with a size > 64KiB, the block
// cannot have HashIndex. So the footer will directly interpreted as
// num_restarts.
//
// Such check is for backward compatibility. We can ensure legacy block
// with a vary large num_restarts i.e. >= 0x80000000 can be interpreted
// correctly as no HashIndex even if the MSB of num_restarts is set.
return num_restarts;
}
BlockBasedTableOptions::DataBlockIndexType index_type;
UnPackIndexTypeAndNumRestarts(block_footer, &index_type, &num_restarts);
return num_restarts;
}
BlockBasedTableOptions::DataBlockIndexType Block::IndexType() const {
assert(size_ >= 2 * sizeof(uint32_t));
if (size_ > kMaxBlockSizeSupportedByHashIndex) {
// The check is for the same reason as that in NumRestarts()
return BlockBasedTableOptions::kDataBlockBinarySearch;
}
uint32_t block_footer = DecodeFixed32(data_ + size_ - sizeof(uint32_t));
uint32_t num_restarts = block_footer;
BlockBasedTableOptions::DataBlockIndexType index_type;
UnPackIndexTypeAndNumRestarts(block_footer, &index_type, &num_restarts);
return index_type;
}
Block::~Block() {
// This sync point can be re-enabled if RocksDB can control the
// initialization order of any/all static options created by the user.
// TEST_SYNC_POINT("Block::~Block");
}
Block::Block(BlockContents&& contents, size_t read_amp_bytes_per_bit,
Statistics* statistics)
: contents_(std::move(contents)),
data_(contents_.data.data()),
size_(contents_.data.size()),
restart_offset_(0),
num_restarts_(0) {
TEST_SYNC_POINT("Block::Block:0");
if (size_ < sizeof(uint32_t)) {
size_ = 0; // Error marker
} else {
// Should only decode restart points for uncompressed blocks
num_restarts_ = NumRestarts();
switch (IndexType()) {
case BlockBasedTableOptions::kDataBlockBinarySearch:
restart_offset_ = static_cast<uint32_t>(size_) -
(1 + num_restarts_) * sizeof(uint32_t);
if (restart_offset_ > size_ - sizeof(uint32_t)) {
// The size is too small for NumRestarts() and therefore
// restart_offset_ wrapped around.
size_ = 0;
}
break;
case BlockBasedTableOptions::kDataBlockBinaryAndHash:
if (size_ < sizeof(uint32_t) /* block footer */ +
sizeof(uint16_t) /* NUM_BUCK */) {
size_ = 0;
break;
}
uint16_t map_offset;
data_block_hash_index_.Initialize(
contents.data.data(),
static_cast<uint16_t>(contents.data.size() -
sizeof(uint32_t)), /*chop off
NUM_RESTARTS*/
&map_offset);
restart_offset_ = map_offset - num_restarts_ * sizeof(uint32_t);
if (restart_offset_ > map_offset) {
// map_offset is too small for NumRestarts() and
// therefore restart_offset_ wrapped around.
size_ = 0;
break;
}
break;
default:
size_ = 0; // Error marker
}
}
if (read_amp_bytes_per_bit != 0 && statistics && size_ != 0) {
read_amp_bitmap_.reset(new BlockReadAmpBitmap(
restart_offset_, read_amp_bytes_per_bit, statistics));
}
}
MetaBlockIter* Block::NewMetaIterator(bool block_contents_pinned) {
MetaBlockIter* iter = new MetaBlockIter();
if (size_ < 2 * sizeof(uint32_t)) {
iter->Invalidate(Status::Corruption("bad block contents"));
return iter;
} else if (num_restarts_ == 0) {
// Empty block.
iter->Invalidate(Status::OK());
} else {
iter->Initialize(data_, restart_offset_, num_restarts_,
block_contents_pinned);
}
return iter;
}
DataBlockIter* Block::NewDataIterator(const Comparator* raw_ucmp,
SequenceNumber global_seqno,
DataBlockIter* iter, Statistics* stats,
bool block_contents_pinned) {
DataBlockIter* ret_iter;
if (iter != nullptr) {
ret_iter = iter;
} else {
ret_iter = new DataBlockIter;
}
if (size_ < 2 * sizeof(uint32_t)) {
ret_iter->Invalidate(Status::Corruption("bad block contents"));
return ret_iter;
}
if (num_restarts_ == 0) {
// Empty block.
ret_iter->Invalidate(Status::OK());
return ret_iter;
} else {
ret_iter->Initialize(
raw_ucmp, data_, restart_offset_, num_restarts_, global_seqno,
read_amp_bitmap_.get(), block_contents_pinned,
data_block_hash_index_.Valid() ? &data_block_hash_index_ : nullptr);
if (read_amp_bitmap_) {
if (read_amp_bitmap_->GetStatistics() != stats) {
// DB changed the Statistics pointer, we need to notify read_amp_bitmap_
read_amp_bitmap_->SetStatistics(stats);
}
}
}
return ret_iter;
}
IndexBlockIter* Block::NewIndexIterator(
const Comparator* raw_ucmp, SequenceNumber global_seqno,
IndexBlockIter* iter, Statistics* /*stats*/, bool total_order_seek,
bool have_first_key, bool key_includes_seq, bool value_is_full,
bool block_contents_pinned, BlockPrefixIndex* prefix_index) {
IndexBlockIter* ret_iter;
if (iter != nullptr) {
ret_iter = iter;
} else {
ret_iter = new IndexBlockIter;
}
if (size_ < 2 * sizeof(uint32_t)) {
ret_iter->Invalidate(Status::Corruption("bad block contents"));
return ret_iter;
}
if (num_restarts_ == 0) {
// Empty block.
ret_iter->Invalidate(Status::OK());
return ret_iter;
} else {
BlockPrefixIndex* prefix_index_ptr =
total_order_seek ? nullptr : prefix_index;
ret_iter->Initialize(raw_ucmp, data_, restart_offset_, num_restarts_,
global_seqno, prefix_index_ptr, have_first_key,
key_includes_seq, value_is_full,
block_contents_pinned);
}
return ret_iter;
}
size_t Block::ApproximateMemoryUsage() const {
size_t usage = usable_size();
#ifdef ROCKSDB_MALLOC_USABLE_SIZE
usage += malloc_usable_size((void*)this);
#else
usage += sizeof(*this);
#endif // ROCKSDB_MALLOC_USABLE_SIZE
if (read_amp_bitmap_) {
usage += read_amp_bitmap_->ApproximateMemoryUsage();
}
return usage;
}
} // namespace ROCKSDB_NAMESPACE