From 6a22cbceaf49d2902071fbc4235507eccd9f2629 Mon Sep 17 00:00:00 2001
From: Tomasz Grabiec <tgrabiec@scylladb.com>
Date: Mon, 3 Jul 2017 14:04:36 +0200
Subject: [PATCH] row_cache: Add metrics for operations on underlying reader

---
 read_context.hh | 13 +++++++++++--
 row_cache.cc    |  3 +++
 row_cache.hh    |  3 +++
 3 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/read_context.hh b/read_context.hh
index 7adde6ea54..a67fe09eb6 100644
--- a/read_context.hh
+++ b/read_context.hh
@@ -71,6 +71,9 @@ public:
                 _range = std::move(*new_range);
                 _last_key = {};
             }
+            if (_reader) {
+                ++_cache._tracker._stats.underlying_recreations;
+            }
             auto& snap = _cache.snapshot_for_phase(phase);
             _reader = _cache.create_underlying_reader(_read_context, snap, _range);
             _reader_creation_phase = phase;
@@ -90,8 +93,13 @@ public:
         _range = std::move(range);
         _last_key = { };
         _new_last_key = { };
-        if (_reader && _reader_creation_phase == phase) {
-            return _reader->fast_forward_to(_range);
+        if (_reader) {
+            if (_reader_creation_phase == phase) {
+                ++_cache._tracker._stats.underlying_partition_skips;
+                return _reader->fast_forward_to(_range);
+            } else {
+                ++_cache._tracker._stats.underlying_recreations;
+            }
         }
         _reader = _cache.create_underlying_reader(_read_context, snapshot, _range);
         _reader_creation_phase = phase;
@@ -211,6 +219,7 @@ public:
     // Fast forwards the underlying streamed_mutation to given range.
     future<> fast_forward_to(position_range range) {
         return ensure_sm_created().then([this, range = std::move(range)] () mutable {
+            ++_cache._tracker._stats.underlying_row_skips;
             return _sm->fast_forward_to(std::move(range));
         });
     }
diff --git a/row_cache.cc b/row_cache.cc
index 77d6c770fa..350acb2642 100644
--- a/row_cache.cc
+++ b/row_cache.cc
@@ -111,6 +111,9 @@ cache_tracker::setup_metrics() {
         sm::make_derive("reads", sm::description("number of started reads"), _stats.reads),
         sm::make_derive("reads_with_misses", sm::description("number of reads which had to read from sstables"), _stats.reads_with_misses),
         sm::make_gauge("active_reads", sm::description("number of currently active reads"), [this] { return _stats.active_reads(); }),
+        sm::make_derive("sstable_reader_recreations", sm::description("number of times sstable reader was recreated due to memtable flush"), _stats.underlying_recreations),
+        sm::make_derive("sstable_partition_skips", sm::description("number of times sstable reader was fast forwarded across partitions"), _stats.underlying_partition_skips),
+        sm::make_derive("sstable_row_skips", sm::description("number of times sstable reader was fast forwarded within a partition"), _stats.underlying_row_skips),
     });
 }
 
diff --git a/row_cache.hh b/row_cache.hh
index d1e2df1549..1425e95f65 100644
--- a/row_cache.hh
+++ b/row_cache.hh
@@ -200,6 +200,9 @@ public:
         uint64_t partitions;
         uint64_t modification_count;
         uint64_t mispopulations;
+        uint64_t underlying_recreations;
+        uint64_t underlying_partition_skips;
+        uint64_t underlying_row_skips;
         uint64_t reads;
         uint64_t reads_with_misses;
         uint64_t reads_done;