From ec28a6971bf0b780548b7417bac98fe4b669b542 Mon Sep 17 00:00:00 2001
From: Aaron <aaron@10gen.com>
Date: Wed, 7 Jul 2010 22:25:09 -0700
Subject: [PATCH] SERVER-366 don't drop referenced key

---
 db/btree.cpp           |  8 ++++----
 dbtests/btreetests.cpp | 33 ++++++++++++++++++++++++++++++++-
 2 files changed, 36 insertions(+), 5 deletions(-)

diff --git a/db/btree.cpp b/db/btree.cpp
index 4ea5327fc51..3610c1dbe92 100644
--- a/db/btree.cpp
+++ b/db/btree.cpp
@@ -310,13 +310,13 @@ namespace mongo {
         topSize = 0;
         int i = 0;
         for ( int j = 0; j < n; j++ ) {
-            if( j > 0 && k( j ).isUnused() && k( j ).prevChildBucket.isNull() ) {
-                if ( i < refPos ) {
-                    --refPos;
-                }
+            if( j > 0 && ( j != refPos ) && k( j ).isUnused() && k( j ).prevChildBucket.isNull() ) {
                 continue; // key is unused and has no children - drop it
             }
             if( i != j ) {
+                if ( j == refPos ) {
+                    refPos = i; // i < j so j will never be refPos again
+                }
                 k( i ) = k( j );
             }
             short ofsold = k(i).keyDataOfs();
diff --git a/dbtests/btreetests.cpp b/dbtests/btreetests.cpp
index 0607deeb5e7..a90a0975c88 100644
--- a/dbtests/btreetests.cpp
+++ b/dbtests/btreetests.cpp
@@ -322,7 +322,7 @@ namespace BtreeTests {
 
             ASSERT( unused2 < unused );
         }
-    private:
+    protected:
         void insert( long long n ) {
             string val( 800, ' ' );
             for( int i = 0; i < 800; i += 8 ) {
@@ -337,6 +337,36 @@ namespace BtreeTests {
         }        
     };
 
+    class DontDropReferenceKey : public PackUnused {
+    public:
+        void run() {
+            // with 80 root node is full
+            for ( long long i = 0; i < 80; i += 1 ) {
+                insert( i );
+            }
+            
+            BSONObjBuilder start;
+            start.appendMinKey( "a" );
+            BSONObjBuilder end;
+            end.appendMaxKey( "a" );
+            BSONObj l = bt()->keyNode( 0 ).key;
+            string toInsert;
+            auto_ptr< BtreeCursor > c( new BtreeCursor( nsdetails( ns() ), 1, id(), start.done(), end.done(), false, 1 ) );
+            while( c->ok() ) {
+                if ( c->currKey().woCompare( l ) > 0 ) {
+                    toInsert = c->currKey().firstElement().valuestr();
+                    break;
+                }
+                c->advance();
+            }
+            // too much work to try to make this happen through inserts and deletes
+            const_cast< DiskLoc& >( bt()->keyNode( 1 ).prevChildBucket ) = DiskLoc();
+            const_cast< DiskLoc& >( bt()->keyNode( 1 ).recordLoc ).GETOFS() |= 1; // make unused
+            BSONObj k = BSON( "a" << toInsert );
+            Base::insert( k );
+        }
+    };
+    
     class All : public Suite {
     public:
         All() : Suite( "btree" ){
@@ -352,6 +382,7 @@ namespace BtreeTests {
             add< SERVER983 >();
             add< ReuseUnused >();
             add< PackUnused >();
+            add< DontDropReferenceKey >();
         }
     } myall;
 }