SERVER-18829 Have pages start in the middle of the LRU queue for eviction.

(cherry picked from commit d57dc26729bbc59c5bc3928aa90bb2ac3cd15d6d)

2 files changed, 18 insertions, 3 deletions

diff --git a/src/include/cache.h b/src/include/cache.h
index 11f631416af..58b7b4dbddb 100644
--- a/src/include/cache.h
+++ b/src/include/cache.h
@@ -71,6 +71,8 @@ struct __wt_cache {
 	 * Read information.
 	 */
 	uint64_t   read_gen;		/* Page read generation (LRU) */
+	uint64_t   read_gen_oldest;	/* The oldest read generation that
+					   eviction knows about */
 
 	/*
 	 * Eviction thread information.
diff --git a/src/include/cache.i b/src/include/cache.i
index f952f1bf698..d84069c43fb 100644
--- a/src/include/cache.i
+++ b/src/include/cache.i
@@ -27,11 +27,11 @@ __wt_cache_read_gen_incr(WT_SESSION_IMPL *session)
 }
 
 /*
- * __wt_cache_read_gen_set --
- *      Get the read generation to store in a page.
+ * __wt_cache_read_gen_bump --
+ *      Get the read generation to keep a page in memory.
  */
 static inline uint64_t
-__wt_cache_read_gen_set(WT_SESSION_IMPL *session)
+__wt_cache_read_gen_bump(WT_SESSION_IMPL *session)
 {
 	/*
 	 * We return read-generations from the future (where "the future" is
@@ -46,6 +46,19 @@ __wt_cache_read_gen_set(WT_SESSION_IMPL *session)
 }
 
 /*
+ * __wt_cache_read_gen_new --
+ *      Get the read generation for a new page in memory.
+ */
+static inline uint64_t
+__wt_cache_read_gen_new(WT_SESSION_IMPL *session)
+{
+	WT_CACHE *cache;
+
+	cache = S2C(session)->cache;
+	return (__wt_cache_read_gen(session) + cache->read_gen_oldest) / 2;
+}
+
+/*
  * __wt_cache_pages_inuse --
  *	Return the number of pages in use.
  */