Replace per-shard chained hash tables with open-addressing scheme (#1…

…0194)

Summary:
In FastLRUCache, we replace the current chained per-shard hash table by an open-addressing hash table. In particular, this allows us to preallocate all handles.

Because all handles are preallocated, this implementation doesn't support strict_capacity_limit = false (i.e., allowing insertions beyond the predefined capacity). This clashes with current assumptions of some tests, namely two tests in cache_test and the crash tests. We have disabled these for now.

Pull Request resolved: #10194

Test Plan: ``make -j24 check``

Reviewed By: pdillinger

Differential Revision: D37296770

Pulled By: guidotag

fbshipit-source-id: 232ff1b8260331d868ebf4e3e5d8ad709390b0ad

cache/cache_test.cc

@@ -650,6 +650,10 @@ TEST_P(CacheTest, ReleaseWithoutErase) {
 }
 
 TEST_P(CacheTest, SetCapacity) {
+  if (GetParam() == kFast) {
+    ROCKSDB_GTEST_BYPASS("FastLRUCache doesn't support capacity adjustments.");
+    return;
+  }
   // test1: increase capacity
   // lets create a cache with capacity 5,
   // then, insert 5 elements, then increase capacity
@@ -698,6 +702,12 @@ TEST_P(CacheTest, SetCapacity) {
 }
 
 TEST_P(LRUCacheTest, SetStrictCapacityLimit) {
+  if (GetParam() == kFast) {
+    ROCKSDB_GTEST_BYPASS(
+        "FastLRUCache doesn't support an unbounded number of inserts beyond "
+        "capacity.");
+    return;
+  }
   // test1: set the flag to false. Insert more keys than capacity. See if they
   // all go through.
   std::shared_ptr<Cache> cache = NewCache(5, 0, false);
@@ -749,6 +759,10 @@ TEST_P(LRUCacheTest, SetStrictCapacityLimit) {
 }
 
 TEST_P(CacheTest, OverCapacity) {
+  if (GetParam() == kFast) {
+    ROCKSDB_GTEST_BYPASS("FastLRUCache doesn't support capacity adjustments.");
+    return;
+  }
   size_t n = 10;
 
   // a LRUCache with n entries and one shard only