Cap automatic arena block size to 1 MB (#7907)

Summary:
Larger arena block size does provide the benefit of reducing allocation overhead, however it may cause other troubles. For example, allocator is more likely not to allocate them to physical memory and trigger page fault. Weighing the risk, we cap the arena block size to 1MB. Users can always use a larger value if they want.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7907

Test Plan: Run all existing tests

Reviewed By: pdillinger

Differential Revision: D26135269

fbshipit-source-id: b7f55afd03e6ee1d8715f90fa11b6c33944e9ea8

HISTORY.md

@@ -22,6 +22,9 @@
 * The `skip_filters` parameter to SstFileWriter is now considered deprecated. Use `BlockBasedTableOptions::filter_policy` to control generation of filters.
 * ClockCache is known to have bugs that could lead to crash or corruption, so should not be used until fixed. Use NewLRUCache instead.
 
+### Default Option Change
+* When options.arena_block_size <= 0 (default value 0), still use writer_buffer_size / 8 but cap to 1MB. Too large alloation size might not be friendly to allocator and might cause performance issues in extreme cases.
+
 ## 6.20.0 (04/16/2021)
 ### Behavior Changes
 * `ColumnFamilyOptions::sample_for_compression` now takes effect for creation of all block-based tables. Previously it only took effect for block-based tables created by flush.

db/column_family.cc

@@ -214,7 +214,8 @@ ColumnFamilyOptions SanitizeOptions(const ImmutableDBOptions& db_options,
   // if user sets arena_block_size, we trust user to use this value. Otherwise,
   // calculate a proper value from writer_buffer_size;
   if (result.arena_block_size <= 0) {
-    result.arena_block_size = result.write_buffer_size / 8;
+    result.arena_block_size =
+        std::min(size_t{1024 * 1024}, result.write_buffer_size / 8);
 
     // Align up to 4k
     const size_t align = 4 * 1024;

db/column_family_test.cc

@@ -2286,6 +2286,8 @@ TEST_P(ColumnFamilyTest, SanitizeOptions) {
               // not a multiple of 4k, round up 4k
               expected_arena_block_size += 4 * 1024;
             }
+            expected_arena_block_size =
+                std::min(size_t{1024 * 1024}, expected_arena_block_size);
             ASSERT_EQ(expected_arena_block_size, result.arena_block_size);
           }
         }

include/rocksdb/advanced_options.h

@@ -390,7 +390,8 @@ struct AdvancedColumnFamilyOptions {
 
   // size of one block in arena memory allocation.
   // If <= 0, a proper value is automatically calculated (usually 1/8 of
-  // writer_buffer_size, rounded up to a multiple of 4KB).
+  // writer_buffer_size, rounded up to a multiple of 4KB, or 1MB which ever is
+  // smaller).
   //
   // There are two additional restriction of the specified size:
   // (1) size should be in the range of [4096, 2 << 30] and