From 0b4ef0d4117827353fa2da04c48db15530b9effc Mon Sep 17 00:00:00 2001
From: Tony Sun <tony.sun@cloudant.com>
Date: Wed, 10 May 2017 21:16:13 -0700
Subject: add compaction logging

To predict future compaction results, we log pre-compaction and
post-compaction file sizes. These log results will be used as data
points for regression analysis.

COUCHDB-3417
---
 src/couch/src/couch_db_updater.erl              |  9 ++++++---
 src/couch_mrview/src/couch_mrview_compactor.erl | 11 ++++++++++-
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/src/couch/src/couch_db_updater.erl b/src/couch/src/couch_db_updater.erl
index 78726358e..bb8e9dafb 100644
--- a/src/couch/src/couch_db_updater.erl
+++ b/src/couch/src/couch_db_updater.erl
@@ -218,7 +218,7 @@ handle_cast(start_compact, Db) ->
         % compact currently running, this is a no-op
         {noreply, Db}
     end;
-handle_cast({compact_done, CompactFilepath}, #db{filepath=Filepath}=Db) ->
+handle_cast({compact_done, CompactFilepath}, #db{filepath=Filepath,fd=Fd}=Db) ->
     {ok, NewFd} = couch_file:open(CompactFilepath),
     {ok, NewHeader0} = couch_file:read_header(NewFd),
     NewHeader = couch_db_header:set(NewHeader0, [
@@ -242,8 +242,11 @@ handle_cast({compact_done, CompactFilepath}, #db{filepath=Filepath}=Db) ->
             revs_limit = Db#db.revs_limit
         }),
 
-        couch_log:debug("CouchDB swapping files ~s and ~s.",
-                        [Filepath, CompactFilepath]),
+        {ok, Pre} = couch_file:bytes(Fd),
+        {ok, Post} = couch_file:bytes(NewFd),
+
+        couch_log:notice("Compaction swap for db: ~s ~p ~p", [Filepath,
+                Pre, Post]),
         ok = file:rename(CompactFilepath, Filepath ++ ".compact"),
         RootDir = config:get("couchdb", "database_dir", "."),
         couch_file:delete(RootDir, Filepath),
diff --git a/src/couch_mrview/src/couch_mrview_compactor.erl b/src/couch_mrview/src/couch_mrview_compactor.erl
index fabe2894c..c1b2fbc21 100644
--- a/src/couch_mrview/src/couch_mrview_compactor.erl
+++ b/src/couch_mrview/src/couch_mrview_compactor.erl
@@ -274,9 +274,13 @@ update_task(VID, #acc{changes=Changes, total_changes=Total}=Acc, ChangesInc) ->
 
 
 swap_compacted(OldState, NewState) ->
+    #mrst{
+        fd = Fd
+    } = OldState,
     #mrst{
         sig=Sig,
-        db_name=DbName
+        db_name=DbName,
+        fd=NewFd
     } = NewState,
 
     link(NewState#mrst.fd),
@@ -285,6 +289,11 @@ swap_compacted(OldState, NewState) ->
     RootDir = couch_index_util:root_dir(),
     IndexFName = couch_mrview_util:index_file(DbName, Sig),
     CompactFName = couch_mrview_util:compaction_file(DbName, Sig),
+
+    {ok, Pre} = couch_file:bytes(Fd),
+    {ok, Post} = couch_file:bytes(NewFd),
+    couch_log:notice("Compaction swap for view ~s ~p ~p", [IndexFName,
+        Pre, Post]),
     ok = couch_file:delete(RootDir, IndexFName),
     ok = file:rename(CompactFName, IndexFName),
 
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