core: Record change in size after defrag

For JSON type, after defrag size may change. The page usage object
carries this change out to a higher call level where the db stats can be
updated.

Signed-off-by: Abhijat Malviya <[email protected]>

Author: abhijat

src/core/page_usage_stats.cc

@@ -179,4 +179,14 @@ bool PageUsage::ConsumePageStats(mi_page_usage_stats_t stat) {
   return force_reallocate_ || should_reallocate;
 }
 
+void PageUsage::RecordChangeInSize(const unsigned object_type, const ssize_t delta) {
+  last_delta_ = {object_type, delta};
+}
+
+PageUsage::TypeAndDelta PageUsage::FetchAndResetDelta() {
+  const auto delta = last_delta_;
+  last_delta_ = {0, 0};
+  return delta;
+}
+
 }  // namespace dfly

src/core/page_usage_stats.h

@@ -41,6 +41,8 @@ struct CollectedPageStats {
 };
 
 class PageUsage {
+  using TypeAndDelta = std::pair<unsigned, ssize_t>;
+
  public:
   PageUsage(CollectPageStats collect_stats, float threshold);
 
@@ -66,6 +68,12 @@ class PageUsage {
     force_reallocate_ = force_reallocate;
   }
 
+  // Record change in size for the last object defragmented. Primarily for use in defragmenting JSON
+  // objects.
+  void RecordChangeInSize(unsigned object_type, ssize_t delta);
+
+  TypeAndDelta FetchAndResetDelta();
+
  private:
   CollectPageStats collect_stats_{CollectPageStats::NO};
   float threshold_;
@@ -93,6 +101,8 @@ class PageUsage {
 
   // For use in testing, forces reallocate check to always return true
   bool force_reallocate_{false};
+
+  TypeAndDelta last_delta_;
 };
 
 }  // namespace dfly