andreacavalli/rocksdb
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Fix a bug that Prev() can hang.

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Summary: Prev() now can hang when there is a key with more than max_skipped number of appearance internally but all of them are newer than the sequence ID to seek. Add unit tests to confirm the bug and fix it.

Test Plan: make all check

Reviewers: igor, haobo

Reviewed By: igor

CC: ljin, yhchiang, leveldb

Differential Revision: https://reviews.facebook.net/D16899
This commit is contained in:
sdong 2014-03-14 16:06:38 -07:00
parent f9d0530213
commit c61c9830d4
2 changed files with 76 additions and 3 deletions
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10
db/db_iter.cc
View File

@ -379,10 +379,10 @@ void DBIter::FindPrevUserEntry() {
uint64_t num_skipped = 0;
ValueType value_type = kTypeDeletion;
bool saved_key_valid = true;
if (iter_->Valid()) {
do {
ParsedInternalKey ikey;
bool saved_key_cleared = false;
if (ParseKey(&ikey) && ikey.sequence <= sequence_) {
if ((value_type != kTypeDeletion) &&
user_comparator_->Compare(ikey.user_key, saved_key_) < 0) {
@ -393,7 +393,7 @@ void DBIter::FindPrevUserEntry() {
if (value_type == kTypeDeletion) {
saved_key_.clear();
ClearSavedValue();
saved_key_cleared = true;
saved_key_valid = false;
} else {
Slice raw_value = iter_->value();
if (saved_value_.capacity() > raw_value.size() + 1048576) {
@ -403,13 +403,17 @@ void DBIter::FindPrevUserEntry() {
SaveKey(ExtractUserKey(iter_->key()), &saved_key_);
saved_value_.assign(raw_value.data(), raw_value.size());
}
} else {
// In the case of ikey.sequence > sequence_, we might have already
// iterated to a different user key.
saved_key_valid = false;
}
num_skipped++;
// If we have sequentially iterated via numerous keys and still not
// found the prev user-key, then it is better to seek so that we can
// avoid too many key comparisons. We seek to the first occurence of
// our current key by looking for max sequence number.
if (!saved_key_cleared && num_skipped > max_skip_) {
if (saved_key_valid && num_skipped > max_skip_) {
num_skipped = 0;
std::string last_key;
AppendInternalKey(&last_key,

69
db/db_test.cc
View File

@ -1368,6 +1368,75 @@ TEST(DBTest, IterSeekBeforePrev) {
delete iter;
}
TEST(DBTest, IterNextWithNewerSeq) {
ASSERT_OK(Put("0", "0"));
dbfull()->Flush(FlushOptions());
ASSERT_OK(Put("a", "b"));
ASSERT_OK(Put("c", "d"));
ASSERT_OK(Put("d", "e"));
auto iter = db_->NewIterator(ReadOptions());
// Create a key that needs to be skipped for Seq too new
for (uint64_t i = 0; i < last_options_.max_sequential_skip_in_iterations + 1;
i++) {
ASSERT_OK(Put("b", "f"));
}
iter->Seek(Slice("a"));
ASSERT_EQ(IterStatus(iter), "a->b");
iter->Next();
ASSERT_EQ(IterStatus(iter), "c->d");
delete iter;
}
TEST(DBTest, IterPrevWithNewerSeq) {
ASSERT_OK(Put("0", "0"));
dbfull()->Flush(FlushOptions());
ASSERT_OK(Put("a", "b"));
ASSERT_OK(Put("c", "d"));
ASSERT_OK(Put("d", "e"));
auto iter = db_->NewIterator(ReadOptions());
// Create a key that needs to be skipped for Seq too new
for (uint64_t i = 0; i < last_options_.max_sequential_skip_in_iterations + 1;
i++) {
ASSERT_OK(Put("b", "f"));
}
iter->Seek(Slice("d"));
ASSERT_EQ(IterStatus(iter), "d->e");
iter->Prev();
ASSERT_EQ(IterStatus(iter), "c->d");
iter->Prev();
ASSERT_EQ(IterStatus(iter), "a->b");
iter->Prev();
delete iter;
}
TEST(DBTest, IterPrevWithNewerSeq2) {
ASSERT_OK(Put("0", "0"));
dbfull()->Flush(FlushOptions());
ASSERT_OK(Put("a", "b"));
ASSERT_OK(Put("c", "d"));
ASSERT_OK(Put("d", "e"));
auto iter = db_->NewIterator(ReadOptions());
iter->Seek(Slice("c"));
ASSERT_EQ(IterStatus(iter), "c->d");
// Create a key that needs to be skipped for Seq too new
for (uint64_t i = 0; i < last_options_.max_sequential_skip_in_iterations + 1;
i++) {
ASSERT_OK(Put("b", "f"));
}
iter->Prev();
ASSERT_EQ(IterStatus(iter), "a->b");
iter->Prev();
delete iter;
}
TEST(DBTest, IterEmpty) {
do {
Iterator* iter = db_->NewIterator(ReadOptions());