From 74686b1380eecd220eacbbcfe0fb95377d708ec8 Mon Sep 17 00:00:00 2001
From: Kresten Krab Thorup <krab@trifork.com>
Date: Mon, 30 Apr 2012 21:28:33 +0200
Subject: [PATCH] Implement merge hibernation for tail scan

When scanning just one file (because all it's keys
are after the ones in the other file), we also
can need hibernation to save memory.  Especially
the bloom filters being built take a lot of mem.
---
 src/hanoi_merger.erl | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/src/hanoi_merger.erl b/src/hanoi_merger.erl
index 0069b16..ddc7c18 100644
--- a/src/hanoi_merger.erl
+++ b/src/hanoi_merger.erl
@@ -155,6 +155,16 @@ scan(BT1, BT2, Out, IsLastLevel, [{Key1,Value1}|AT]=AKVs, [{Key2,Value2}|BT]=BKV
             scan(BT1, BT2, Out2, IsLastLevel, AT, BT, Count+1, step(Step, 2))
     end.
 
+
+hibernate_scan_only(Keep) ->
+    erlang:garbage_collect(),
+    receive
+        {step, From, HowMany} ->
+            {BT, OutBin, IsLastLevel, KVs, Count, N} = erlang:binary_to_term( zlib:gunzip( Keep ) ),
+            scan_only(BT, hanoi_writer:deserialize(OutBin), IsLastLevel, KVs, Count, {N+HowMany, From})
+    end.
+
+
 scan_only(BT, Out, IsLastLevel, KVs, Count, {N, FromPID}) when N < 1, KVs =/= [] ->
     case FromPID of
         none ->
@@ -166,6 +176,10 @@ scan_only(BT, Out, IsLastLevel, KVs, Count, {N, FromPID}) when N < 1, KVs =/= []
     receive
         {step, From, HowMany} ->
             scan_only(BT, Out, IsLastLevel, KVs, Count, {N+HowMany, From})
+    after 10000 ->
+            Args = {BT, hanoi_writer:serialize(Out), IsLastLevel, KVs, Count, N},
+            Keep = zlib:gzip ( erlang:term_to_binary( Args ) ),
+            hibernate_scan_only(Keep);
     end;
 
 scan_only(BT, Out, IsLastLevel, [], Count, {_, FromPID}=Step) ->