Mapping table fix to avoid preallocating memory (cmu-db#1190)

* Adding new mapping table

* Revert "Fixing non-unique key insert problem"

This reverts commit 4267752.

* Revert LOG_INFO to LOG_TRACE

* Fix segment fault problem by moving munmap() to after ~EpochManager()

* Avoid compiler error

* Enhance log message for mmap()'ed mapping table

Author: wangziqi2013

src/include/index/bwtree.h

@@ -35,6 +35,8 @@
 #include <cstddef>
 #include <vector>
 
+#include <sys/mman.h>
+
 /*
  * BWTREE_PELOTON - Specifies whether Peloton-specific features are
  *                  Compiled or not
@@ -2864,6 +2866,21 @@ class BwTree : public BwTreeBase {
    * the mapping table rather than CAS with nullptr
    */
   void InitMappingTable() {
+    mapping_table = (std::atomic<const BaseNode *> *) \
+                    mmap(NULL, 1024 * 1024 * 1024, 
+                         PROT_READ | PROT_WRITE, 
+                         MAP_ANONYMOUS | MAP_PRIVATE,
+                         -1, 0);
+    // If allocation fails, we throw an error because this is uncoverable
+    // The upper level functions should either catch this exception
+    // and then use another index instead, or simply kill the system
+    if(mapping_table == (void *)-1) {
+      LOG_ERROR("Failed to initialize mapping table");
+      throw IndexException("mmap() failed to initialize mapping table for Bw-Tree");
+    }
+
+    LOG_TRACE("Mapping table allocated via mmap()");
+
     LOG_TRACE("Initializing mapping table.... size = %lu", MAPPING_TABLE_SIZE);
     LOG_TRACE("Fast initialization: Do not set to zero");
 
@@ -7379,7 +7396,7 @@ class BwTree : public BwTreeBase {
   NodeID first_leaf_id;
 
   std::atomic<NodeID> next_unused_node_id;
-  std::array<std::atomic<const BaseNode *>, MAPPING_TABLE_SIZE> mapping_table;
+  std::atomic<const BaseNode *> *mapping_table;
 
   // This list holds free NodeID which was removed by remove delta
   // We recycle NodeID in epoch manager
@@ -7568,6 +7585,8 @@ class BwTree : public BwTreeBase {
       // would always fail, until we have cleaned all epoch nodes
       current_epoch_p = nullptr;
 
+      LOG_DEBUG("Clearing the epoch in ~EpochManager()...");
+
       // If all threads has exited then all thread counts are
       // 0, and therefore this should proceed way to the end
       ClearEpoch();
@@ -7605,6 +7624,20 @@ class BwTree : public BwTreeBase {
                 epoch_leave.load());
 #endif
 
+      // NOTE: Only unmap memory here because we need to access the mapping
+      // table in the above routine. If it was unmapped in ~BwTree() then this
+      // function will invoke illegal memory access
+      int munmap_ret = munmap(tree_p->mapping_table, 1024 * 1024 * 1024);
+
+      // Although failure of munmap is not fatal, we still print out 
+      // an error log entry
+      // Otherwise just trace log
+      if(munmap_ret != 0) {
+        LOG_ERROR("munmap() returns with %d", munmap_ret);
+      } else {
+        LOG_TRACE("Mapping table is unmapped for Bw-Tree");
+      }
+      
       return;
     }
 

src/index/bwtree_index.cpp

@@ -16,7 +16,7 @@
 #include "index/scan_optimizer.h"
 #include "statistics/stats_aggregator.h"
 #include "settings/settings_manager.h"
-
+ 
 namespace peloton {
 namespace index {