From cb164bfc486b0892cd1ef8c49b5f3614b6bba30d Mon Sep 17 00:00:00 2001
From: Venkatesh Radhakrishnan <rven@fb.com>
Date: Fri, 28 Aug 2015 11:07:07 -0700
Subject: [PATCH] Do not delete iterators for immutable memtables.

Summary:
The immutable memtable iterators are allocated from an arena and there
is no benefit from deleting these. Also the immutable memtables
themselves will continue to be in memory until the version set
containing it is alive. We will not remove immutable memtable iterators
over the upper bound. We now add immutable iterators to the test.

Test Plan: db_tailing_iter_test.TailingIteratorTrimSeekToNext

Reviewers: tnovak, sdong

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D45597
---
 db/db_tailing_iter_test.cc |  7 ++++++-
 db/forward_iterator.cc     | 30 +-----------------------------
 2 files changed, 7 insertions(+), 30 deletions(-)

diff --git a/db/db_tailing_iter_test.cc b/db/db_tailing_iter_test.cc
index 9bce29a43d..93f12a76d0 100644
--- a/db/db_tailing_iter_test.cc
+++ b/db/db_tailing_iter_test.cc
@@ -121,7 +121,12 @@ TEST_F(DBTestTailingIterator, TailingIteratorSeekToNext) {
 }
 
 TEST_F(DBTestTailingIterator, TailingIteratorTrimSeekToNext) {
-  CreateAndReopenWithCF({"pikachu"}, CurrentOptions());
+  const uint64_t k20KB = 20 * 1024;
+  Options options;
+  options.write_buffer_size = k20KB;
+  options.max_write_buffer_number = 6;
+  options.min_write_buffer_number_to_merge = 5;
+  CreateAndReopenWithCF({"pikachu"}, options);
   ReadOptions read_options;
   read_options.tailing = true;
 
diff --git a/db/forward_iterator.cc b/db/forward_iterator.cc
index 2522f56e74..ea493060bc 100644
--- a/db/forward_iterator.cc
+++ b/db/forward_iterator.cc
@@ -238,20 +238,11 @@ void ForwardIterator::SeekInternal(const Slice& internal_key,
     }
     for (size_t i = 0; i < imm_iters_.size(); i++) {
       auto* m = imm_iters_[i];
-      if (!m) {
-        continue;
-      }
       seek_to_first ? m->SeekToFirst() : m->Seek(internal_key);
       if (!m->status().ok()) {
         immutable_status_ = m->status();
       } else if (m->Valid()) {
-        if (!IsOverUpperBound(m->key())) {
-          immutable_min_heap_.push(m);
-        } else {
-          has_iter_trimmed_for_upper_bound_ = true;
-          delete m;
-          imm_iters_[i] = nullptr;
-        }
+        immutable_min_heap_.push(m);
       }
     }
 
@@ -624,19 +615,6 @@ bool ForwardIterator::NeedToRebuildTrimmed(const Slice& target) {
 }
 
 void ForwardIterator::DeleteCurrentIter() {
-  for (size_t i = 0; i < imm_iters_.size(); i++) {
-    auto& m = imm_iters_[i];
-    if (!m) {
-      continue;
-    }
-    if (m == current_) {
-      has_iter_trimmed_for_upper_bound_ = true;
-      delete m;
-      m = nullptr;
-      return;
-    }
-  }
-
   const VersionStorageInfo* vstorage = sv_->current->storage_info();
   const std::vector<FileMetaData*>& l0 = vstorage->LevelFiles(0);
   for (uint32_t i = 0; i < l0.size(); ++i) {
@@ -667,12 +645,6 @@ bool ForwardIterator::TEST_CheckDeletedIters() {
   if (!has_iter_trimmed_for_upper_bound_) {
     return false;
   }
-  for (size_t i = 0; i < imm_iters_.size(); i++) {
-    auto& m = imm_iters_[i];
-    if (!m) {
-      return true;
-    }
-  }
 
   const VersionStorageInfo* vstorage = sv_->current->storage_info();
   const std::vector<FileMetaData*>& l0 = vstorage->LevelFiles(0);