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Revert "DBIter::Next() can skip user key checking if previous entry's seqnum is 0 (#5244)"

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This reverts commit 25d81e4577.
This commit is contained in:
sdong 2019-09-19 10:57:47 -07:00
parent 4525e4bec2
commit f633994fef
2 changed files with 3 additions and 27 deletions
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1
HISTORY.md
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@ -2,6 +2,7 @@
## Unreleased
### Bug Fixes
* Fix a bug where the compaction snapshot refresh feature is not disabled as advertised when `snap_refresh_nanos` is set to 0..
* Revert "DBIter::Next() can skip user key checking if previous entry's seqnum is 0", which is not a bug, but can make the previous bug's sympthom more severe.
### Default Option Change
* LRUCacheOptions.high_pri_pool_ratio is set to 0.5 (previously 0.0) by default, which means that by default midpoint insertion is enabled. The same change is made for the default value of high_pri_pool_ratio argument in NewLRUCache(). When block cache is not explictly created, the small block cache created by BlockBasedTable will still has this option to be 0.0.

29
db/db_iter.cc
View File

@ -133,7 +133,6 @@ class DBIter final: public Iterator {
direction_(kForward),
valid_(false),
current_entry_is_merged_(false),
is_key_seqnum_zero_(false),
prefix_same_as_start_(read_options.prefix_same_as_start),
pin_thru_lifetime_(read_options.pin_data),
total_order_seek_(read_options.total_order_seek),
@ -334,10 +333,6 @@ class DBIter final: public Iterator {
Direction direction_;
bool valid_;
bool current_entry_is_merged_;
// True if we know that the current entry's seqnum is 0.
// This information is used as that the next entry will be for another
// user key.
bool is_key_seqnum_zero_;
const bool prefix_same_as_start_;
// Means that we will pin all data blocks we read as long the Iterator
// is not deleted, will be true if ReadOptions::pin_data is true
@ -386,7 +381,6 @@ void DBIter::Next() {
num_internal_keys_skipped_ = 0;
bool ok = true;
if (direction_ == kReverse) {
is_key_seqnum_zero_ = false;
if (!ReverseToForward()) {
ok = false;
}
@ -406,7 +400,6 @@ void DBIter::Next() {
FindNextUserEntry(true /* skipping the current user key */,
prefix_same_as_start_);
} else {
is_key_seqnum_zero_ = false;
valid_ = false;
}
if (statistics_ != nullptr && valid_) {
@ -457,16 +450,10 @@ inline bool DBIter::FindNextUserEntryInternal(bool skipping, bool prefix_check)
is_blob_ = false;
do {
// Will update is_key_seqnum_zero_ as soon as we parsed the current key
// but we need to save the previous value to be used in the loop.
bool is_prev_key_seqnum_zero = is_key_seqnum_zero_;
if (!ParseKey(&ikey_)) {
is_key_seqnum_zero_ = false;
return false;
}
is_key_seqnum_zero_ = (ikey_.sequence == 0);
assert(iterate_upper_bound_ == nullptr || iter_.MayBeOutOfUpperBound() ||
user_comparator_.Compare(ikey_.user_key, *iterate_upper_bound_) < 0);
if (iterate_upper_bound_ != nullptr && iter_.MayBeOutOfUpperBound() &&
@ -485,18 +472,11 @@ inline bool DBIter::FindNextUserEntryInternal(bool skipping, bool prefix_check)
}
if (IsVisible(ikey_.sequence)) {
// If the previous entry is of seqnum 0, the current entry will not
// possibly be skipped. This condition can potentially be relaxed to
// prev_key.seq <= ikey_.sequence. We are cautious because it will be more
// prone to bugs causing the same user key with the same sequence number.
if (!is_prev_key_seqnum_zero && skipping &&
user_comparator_.Compare(ikey_.user_key, saved_key_.GetUserKey()) <=
0) {
if (skipping && user_comparator_.Compare(ikey_.user_key,
saved_key_.GetUserKey()) <= 0) {
num_skipped++; // skip this entry
PERF_COUNTER_ADD(internal_key_skipped_count, 1);
} else {
assert(!skipping || user_comparator_.Compare(
ikey_.user_key, saved_key_.GetUserKey()) > 0);
num_skipped = 0;
switch (ikey_.type) {
case kTypeDeletion:
@ -617,7 +597,6 @@ inline bool DBIter::FindNextUserEntryInternal(bool skipping, bool prefix_check)
// If we have sequentially iterated via numerous equal keys, then it's
// better to seek so that we can avoid too many key comparisons.
if (num_skipped > max_skip_ && CanReseekToSkip()) {
is_key_seqnum_zero_ = false;
num_skipped = 0;
std::string last_key;
if (skipping) {
@ -1291,7 +1270,6 @@ void DBIter::Seek(const Slice& target) {
status_ = Status::OK();
ReleaseTempPinnedData();
ResetInternalKeysSkippedCounter();
is_key_seqnum_zero_ = false;
SequenceNumber seq = sequence_;
saved_key_.Clear();
@ -1350,7 +1328,6 @@ void DBIter::SeekForPrev(const Slice& target) {
status_ = Status::OK();
ReleaseTempPinnedData();
ResetInternalKeysSkippedCounter();
is_key_seqnum_zero_ = false;
saved_key_.Clear();
// now saved_key is used to store internal key.
saved_key_.SetInternalKey(target, 0 /* sequence_number */,
@ -1418,7 +1395,6 @@ void DBIter::SeekToFirst() {
ReleaseTempPinnedData();
ResetInternalKeysSkippedCounter();
ClearSavedValue();
is_key_seqnum_zero_ = false;
{
PERF_TIMER_GUARD(seek_internal_seek_time);
@ -1471,7 +1447,6 @@ void DBIter::SeekToLast() {
ReleaseTempPinnedData();
ResetInternalKeysSkippedCounter();
ClearSavedValue();
is_key_seqnum_zero_ = false;
{
PERF_TIMER_GUARD(seek_internal_seek_time);