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Avoid malloc in NotFound key status if no message is given.

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Summary:
In some places we have NotFound status created with empty message, but it doesn't avoid a malloc. With this patch, the malloc is avoided for that case.

The motivation of it is that I found in db_bench readrandom test when all keys are not existing, about 4% of the total running time is spent on malloc of Status, plus a similar amount of CPU spent on free of them, which is not necessary.

Test Plan: make all check

Reviewers: dhruba, haobo, igor

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D14691
This commit is contained in:
Siying Dong
2013-12-26 13:49:04 -08:00
parent b40c052bfa
commit 18df47b79a
4 changed files with 64 additions and 60 deletions
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31
include/rocksdb/status.h
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@@ -25,7 +25,7 @@ namespace rocksdb {
class Status {
public:
// Create a success status.
Status() : state_(nullptr) { }
Status() : code_(kOk), state_(nullptr) { }
~Status() { delete[] state_; }
// Copy the specified status.
@@ -39,6 +39,10 @@ class Status {
static Status NotFound(const Slice& msg, const Slice& msg2 = Slice()) {
return Status(kNotFound, msg, msg2);
}
// Fast path for not found without malloc;
static Status NotFound() {
return Status(kNotFound);
}
static Status Corruption(const Slice& msg, const Slice& msg2 = Slice()) {
return Status(kCorruption, msg, msg2);
}
@@ -59,7 +63,7 @@ class Status {
}
// Returns true iff the status indicates success.
bool ok() const { return (state_ == nullptr); }
bool ok() const { return code() == kOk; }
// Returns true iff the status indicates a NotFound error.
bool IsNotFound() const { return code() == kNotFound; }
@@ -87,13 +91,6 @@ class Status {
std::string ToString() const;
private:
// OK status has a nullptr state_. Otherwise, state_ is a new[] array
// of the following form:
// state_[0..3] == length of message
// state_[4] == code
// state_[5..] == message
const char* state_;
enum Code {
kOk = 0,
kNotFound = 1,
@@ -105,20 +102,30 @@ class Status {
kIncomplete = 7
};
Code code() const {
return (state_ == nullptr) ? kOk : static_cast<Code>(state_[4]);
}
// A nullptr state_ (which is always the case for OK) means the message
// is empty.
// of the following form:
// state_[0..3] == length of message
// state_[4..] == message
Code code_;
const char* state_;
Code code() const {
return code_;
}
explicit Status(Code code) : code_(code), state_(nullptr) { }
Status(Code code, const Slice& msg, const Slice& msg2);
static const char* CopyState(const char* s);
};
inline Status::Status(const Status& s) {
code_ = s.code_;
state_ = (s.state_ == nullptr) ? nullptr : CopyState(s.state_);
}
inline void Status::operator=(const Status& s) {
// The following condition catches both aliasing (when this == &s),
// and the common case where both s and *this are ok.
code_ = s.code_;
if (state_ != s.state_) {
delete[] state_;
state_ = (s.state_ == nullptr) ? nullptr : CopyState(s.state_);