From d439451fab490ce0cabc90f2880443c93d9eab12 Mon Sep 17 00:00:00 2001
From: Lei Jin <lei@fb.com>
Date: Thu, 25 Sep 2014 16:45:37 -0700
Subject: [PATCH] delay initialization of cuckoo table iterator

Summary:
cuckoo table iterator creation is quite expensive since it needs to load
all data and sort them. After compaction, RocksDB creates a new iterator
of the new file to make sure it is in good state. That makes the DB
creation quite slow. Delay the iterator db sort to the seek time to
speed it up.

Test Plan: db_bench

Reviewers: igor, yhchiang, sdong

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D23775
---
 table/cuckoo_table_reader.cc | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/table/cuckoo_table_reader.cc b/table/cuckoo_table_reader.cc
index 8c3f58eac..af6fe6e88 100644
--- a/table/cuckoo_table_reader.cc
+++ b/table/cuckoo_table_reader.cc
@@ -191,7 +191,7 @@ class CuckooTableIterator : public Iterator {
   Slice key() const override;
   Slice value() const override;
   Status status() const override { return status_; }
-  void LoadKeysFromReader();
+  void InitIfNeeded();
 
  private:
   struct BucketComparator {
@@ -224,6 +224,7 @@ class CuckooTableIterator : public Iterator {
   const BucketComparator bucket_comparator_;
   void PrepareKVAtCurrIdx();
   CuckooTableReader* reader_;
+  bool initialized_;
   Status status_;
   // Contains a map of keys to bucket_id sorted in key order.
   std::vector<uint32_t> sorted_bucket_ids_;
@@ -240,13 +241,17 @@ CuckooTableIterator::CuckooTableIterator(CuckooTableReader* reader)
   : bucket_comparator_(reader->file_data_, reader->ucomp_,
                        reader->bucket_length_, reader->user_key_length_),
     reader_(reader),
+    initialized_(false),
     curr_key_idx_(kInvalidIndex) {
   sorted_bucket_ids_.clear();
   curr_value_.clear();
   curr_key_.Clear();
 }
 
-void CuckooTableIterator::LoadKeysFromReader() {
+void CuckooTableIterator::InitIfNeeded() {
+  if (initialized_) {
+    return;
+  }
   sorted_bucket_ids_.reserve(reader_->GetTableProperties()->num_entries);
   uint64_t num_buckets = reader_->table_size_ + reader_->cuckoo_block_size_ - 1;
   assert(num_buckets < kInvalidIndex);
@@ -262,19 +267,23 @@ void CuckooTableIterator::LoadKeysFromReader() {
   std::sort(sorted_bucket_ids_.begin(), sorted_bucket_ids_.end(),
             bucket_comparator_);
   curr_key_idx_ = kInvalidIndex;
+  initialized_ = true;
 }
 
 void CuckooTableIterator::SeekToFirst() {
+  InitIfNeeded();
   curr_key_idx_ = 0;
   PrepareKVAtCurrIdx();
 }
 
 void CuckooTableIterator::SeekToLast() {
+  InitIfNeeded();
   curr_key_idx_ = sorted_bucket_ids_.size() - 1;
   PrepareKVAtCurrIdx();
 }
 
 void CuckooTableIterator::Seek(const Slice& target) {
+  InitIfNeeded();
   const BucketComparator seek_comparator(
       reader_->file_data_, reader_->ucomp_,
       reader_->bucket_length_, reader_->user_key_length_,
@@ -362,9 +371,6 @@ Iterator* CuckooTableReader::NewIterator(
     auto iter_mem = arena->AllocateAligned(sizeof(CuckooTableIterator));
     iter = new (iter_mem) CuckooTableIterator(this);
   }
-  if (iter->status().ok()) {
-    iter->LoadKeysFromReader();
-  }
   return iter;
 }