dont skip IO for filter blocks

Summary:
Based on my experience with linkbench, We should not skip loading bloom filter blocks when they are not available in block cache when using Iterator::Seek

Actually I am not sure why this behavior existed in the first place
Closes https://github.com/facebook/rocksdb/pull/2255

Differential Revision: D5010721

Pulled By: maysamyabandeh

fbshipit-source-id: 0af545a06ac4baeecb248706ec34d009c2480ca4

db/db_bloom_filter_test.cc

@@ -798,36 +798,19 @@ TEST_P(BloomStatsTestWithParam, BloomStatsTestWithIter) {
   ASSERT_OK(iter->status());
   ASSERT_TRUE(iter->Valid());
   ASSERT_EQ(value1, iter->value().ToString());
-  if (partition_filters_) {
-    ASSERT_EQ(0, perf_context.bloom_sst_hit_count);   // no_io
-    ASSERT_EQ(0, perf_context.bloom_sst_miss_count);  // no_io
-  } else {
   ASSERT_EQ(1, perf_context.bloom_sst_hit_count);
-  }
 
   iter->Seek(key3);
   ASSERT_OK(iter->status());
   ASSERT_TRUE(iter->Valid());
   ASSERT_EQ(value3, iter->value().ToString());
-  if (partition_filters_) {
-    ASSERT_EQ(0, perf_context.bloom_sst_hit_count);   // no_io
-    ASSERT_EQ(0, perf_context.bloom_sst_miss_count);  // no_io
-  } else {
   ASSERT_EQ(2, perf_context.bloom_sst_hit_count);
-  }
 
   iter->Seek(key2);
   ASSERT_OK(iter->status());
-  if (partition_filters_) {
-    // iter is still valid since filter did not reject the key2
-    ASSERT_TRUE(iter->Valid());
-    ASSERT_EQ(0, perf_context.bloom_sst_hit_count);   // no_io
-    ASSERT_EQ(0, perf_context.bloom_sst_miss_count);  // no_io
-  } else {
   ASSERT_TRUE(!iter->Valid());
   ASSERT_EQ(1, perf_context.bloom_sst_miss_count);
   ASSERT_EQ(2, perf_context.bloom_sst_hit_count);
-  }
 }
 
 INSTANTIATE_TEST_CASE_P(BloomStatsTestWithParam, BloomStatsTestWithParam,

table/block_based_table_reader.cc

@@ -1477,14 +1477,13 @@ bool BlockBasedTable::PrefixMayMatch(const Slice& internal_key) {
   Status s;
 
   // First, try check with full filter
-  const bool no_io = true;
-  auto filter_entry = GetFilter(no_io);
+  auto filter_entry = GetFilter();
   FilterBlockReader* filter = filter_entry.value;
   if (filter != nullptr) {
     if (!filter->IsBlockBased()) {
       const Slice* const const_ikey_ptr = &internal_key;
       may_match =
-          filter->PrefixMayMatch(prefix, kNotValid, no_io, const_ikey_ptr);
+          filter->PrefixMayMatch(prefix, kNotValid, false, const_ikey_ptr);
     } else {
       InternalKey internal_key_prefix(prefix, kMaxSequenceNumber, kTypeValue);
       auto internal_prefix = internal_key_prefix.Encode();