Make dynamic eviction workers the default. #1143

6 files changed, 83 insertions, 31 deletions

diff --git a/dist/api_data.py b/dist/api_data.py
index 30c76d26a84..3f0fabdc3b9 100644
--- a/dist/api_data.py
+++ b/dist/api_data.py
@@ -340,11 +340,16 @@ connection_runtime_config = [
 	Config('eviction_trigger', '95', r'''
 	    trigger eviction when the cache is using this much memory, as a
 	    percentage of the total cache size''', min=10, max=99),
-	Config('eviction_worker_max', '0', r'''
-	    maximum number of additional threads WiredTiger will start to help
-		evict pages from cache. The number of threads currently running
-		will vary depending on the current eviction load''',
-	    min=0, max=20),
+	Config('eviction_thread_max', '3', r'''
+	    maximum number of threads WiredTiger will start to help
+	    evict pages from cache. The number of threads currently running
+	    will vary depending on the current eviction load''',
+	    min=1, max=20),
+	Config('eviction_thread_min', '1', r'''
+	    minimum number of threads WiredTiger will start to help evict
+	    pages from cache. The number of threads currently running will
+	    vary depending on the current eviction load''',
+	    min=1, max=20),
 	Config('shared_cache', '', r'''
 	    shared cache configuration options. A database should configure
 	    either a cache_size or a shared_cache not both''',
diff --git a/src/btree/bt_evict.c b/src/btree/bt_evict.c
index 1cbd100df5a..e360981188b 100644
--- a/src/btree/bt_evict.c
+++ b/src/btree/bt_evict.c
@@ -168,12 +168,25 @@ __evict_server(void *arg)
 		 * If we have caught up and there are more than the minimum
 		 * number of eviction workers running, shut one down.
 		 */
-		if (conn->evict_workers > 2) {
+		if (conn->evict_workers > conn->evict_workers_min) {
+                        WT_TRET(__wt_verbose(session, WT_VERB_EVICTSERVER,
+                            "Stopping evict worker: %"PRIu32"\n",
+                            conn->evict_workers));
 			worker = &conn->evict_workctx[--conn->evict_workers];
 			F_CLR(worker, WT_EVICT_WORKER_RUN);
 			WT_TRET(__wt_cond_signal(
 			    session, cache->evict_waiter_cond));
 			WT_TRET(__wt_thread_join(session, worker->tid));
+			/*
+			 * Flag errors here with a message, but don't shut down
+			 * the eviction server - that's fatal.
+			 */
+			WT_ASSERT(session, ret == 0);
+			if (ret != 0) {
+				(void)__wt_msg(session,
+				    "Error stopping eviction worker: %d", ret);
+				ret = 0;
+			}
 		}
 		F_CLR(cache, WT_EVICT_ACTIVE);
 		WT_ERR(__wt_verbose(session, WT_VERB_EVICTSERVER, "sleeping"));
@@ -238,8 +251,7 @@ __wt_evict_create(WT_CONNECTION_IMPL *conn)
 			WT_RET(__wt_open_internal_session(conn,
 			    "eviction-worker", 0, 0, &workers[i].session));
 			workers[i].id = i;
-			/* Start at most two worker threads initially. */
-			if (i < 2) {
+			if (i < conn->evict_workers_min) {
 				++conn->evict_workers;
 				F_SET(&workers[i], WT_EVICT_WORKER_RUN);
 				WT_RET(__wt_thread_create(
@@ -433,6 +445,9 @@ __evict_pass(WT_SESSION_IMPL *session)
 		/* Start a worker if we have capacity and the cache is full. */
 		if (bytes_inuse > conn->cache_size &&
 		    conn->evict_workers < conn->evict_workers_max) {
+                        WT_RET(__wt_verbose(session, WT_VERB_EVICTSERVER,
+                            "Starting evict worker: %"PRIu32"\n",
+                            conn->evict_workers));
 			worker = &conn->evict_workctx[conn->evict_workers++];
 			F_SET(worker, WT_EVICT_WORKER_RUN);
 			WT_RET(__wt_thread_create(session,
diff --git a/src/config/config_def.c b/src/config/config_def.c
index 74bad4c6375..1b688384286 100644
--- a/src/config/config_def.c
+++ b/src/config/config_def.c
@@ -74,8 +74,9 @@ static const WT_CONFIG_CHECK confchk_connection_reconfigure[] = {
 	{ "error_prefix", "string", NULL, NULL },
 	{ "eviction_dirty_target", "int", "min=10,max=99", NULL },
 	{ "eviction_target", "int", "min=10,max=99", NULL },
+	{ "eviction_thread_max", "int", "min=1,max=20", NULL },
+	{ "eviction_thread_min", "int", "min=1,max=20", NULL },
 	{ "eviction_trigger", "int", "min=10,max=99", NULL },
-	{ "eviction_worker_max", "int", "min=0,max=20", NULL },
 	{ "shared_cache", "category", NULL,
 	     confchk_shared_cache_subconfigs },
 	{ "statistics", "list",
@@ -298,8 +299,9 @@ static const WT_CONFIG_CHECK confchk_wiredtiger_open[] = {
 	{ "error_prefix", "string", NULL, NULL },
 	{ "eviction_dirty_target", "int", "min=10,max=99", NULL },
 	{ "eviction_target", "int", "min=10,max=99", NULL },
+	{ "eviction_thread_max", "int", "min=1,max=20", NULL },
+	{ "eviction_thread_min", "int", "min=1,max=20", NULL },
 	{ "eviction_trigger", "int", "min=10,max=99", NULL },
-	{ "eviction_worker_max", "int", "min=0,max=20", NULL },
 	{ "exclusive", "boolean", NULL, NULL },
 	{ "extensions", "list", NULL, NULL },
 	{ "file_extend", "list", "choices=[\"data\",\"log\"]", NULL },
@@ -370,9 +372,10 @@ static const WT_CONFIG_ENTRY config_entries[] = {
 	{ "connection.reconfigure",
 	  "async=(enabled=0,ops_max=1024,threads=2),cache_size=100MB,"
 	  "checkpoint=(name=\"WiredTigerCheckpoint\",wait=0),error_prefix=,"
-	  "eviction_dirty_target=80,eviction_target=80,eviction_trigger=95,"
-	  "eviction_worker_max=0,shared_cache=(chunk=10MB,name=,reserve=0,"
-	  "size=500MB),statistics=none,statistics_log=(on_close=0,"
+	  "eviction_dirty_target=80,eviction_target=80,"
+	  "eviction_thread_max=3,eviction_thread_min=1,eviction_trigger=95,"
+	  "shared_cache=(chunk=10MB,name=,reserve=0,size=500MB),"
+	  "statistics=none,statistics_log=(on_close=0,"
 	  "path=\"WiredTigerStat.%d.%H\",sources=,"
 	  "timestamp=\"%b %d %H:%M:%S\",wait=0),verbose=",
 	  confchk_connection_reconfigure
@@ -480,15 +483,16 @@ static const WT_CONFIG_ENTRY config_entries[] = {
 	  "async=(enabled=0,ops_max=1024,threads=2),buffer_alignment=-1,"
 	  "cache_size=100MB,checkpoint=(name=\"WiredTigerCheckpoint\","
 	  "wait=0),checkpoint_sync=,create=0,direct_io=,error_prefix=,"
-	  "eviction_dirty_target=80,eviction_target=80,eviction_trigger=95,"
-	  "eviction_worker_max=0,exclusive=0,extensions=,file_extend=,"
-	  "hazard_max=1000,log=(archive=,enabled=0,file_max=100MB,"
-	  "path=\"\"),lsm_merge=,mmap=,multiprocess=0,session_max=100,"
-	  "shared_cache=(chunk=10MB,name=,reserve=0,size=500MB),"
-	  "statistics=none,statistics_log=(on_close=0,"
-	  "path=\"WiredTigerStat.%d.%H\",sources=,"
-	  "timestamp=\"%b %d %H:%M:%S\",wait=0),transaction_sync=(enabled=0"
-	  ",method=fsync),use_environment_priv=0,verbose=",
+	  "eviction_dirty_target=80,eviction_target=80,"
+	  "eviction_thread_max=3,eviction_thread_min=1,eviction_trigger=95,"
+	  "exclusive=0,extensions=,file_extend=,hazard_max=1000,"
+	  "log=(archive=,enabled=0,file_max=100MB,path=\"\"),lsm_merge=,"
+	  "mmap=,multiprocess=0,session_max=100,shared_cache=(chunk=10MB,"
+	  "name=,reserve=0,size=500MB),statistics=none,"
+	  "statistics_log=(on_close=0,path=\"WiredTigerStat.%d.%H\","
+	  "sources=,timestamp=\"%b %d %H:%M:%S\",wait=0),"
+	  "transaction_sync=(enabled=0,method=fsync),use_environment_priv=0"
+	  ",verbose=",
 	  confchk_wiredtiger_open
 	},
 	{ NULL, NULL, NULL }
diff --git a/src/conn/conn_cache.c b/src/conn/conn_cache.c
index d39a8f891d6..746df68758f 100644
--- a/src/conn/conn_cache.c
+++ b/src/conn/conn_cache.c
@@ -55,9 +55,28 @@ __wt_cache_config(WT_CONNECTION_IMPL *conn, const char *cfg[])
 	WT_RET_NOTFOUND_OK(ret);
 
 	if ((ret =
-	    __wt_config_gets(session, cfg, "eviction_worker_max", &cval)) == 0)
+	    __wt_config_gets(session, cfg, "eviction_thread_max", &cval)) == 0)
 		conn->evict_workers_max = (u_int)cval.val;
 	WT_RET_NOTFOUND_OK(ret);
+	if ((ret =
+	    __wt_config_gets(session, cfg, "eviction_thread_min", &cval)) == 0)
+		conn->evict_workers_min = (u_int)cval.val;
+	WT_RET_NOTFOUND_OK(ret);
+
+	if (conn->evict_workers_min > conn->evict_workers_max)
+		WT_RET_MSG(session, EINVAL,
+		    "eviction_thread_min cannot be greater than "
+                    "eviction_thread_max");
+
+        /*
+         * The eviction thread configuration options include the main eviction
+         * thread and workers. Our implementation splits them out. Adjust
+         * for that here.
+         */
+        WT_ASSERT(session,
+            conn->evict_workers_max > 0 && conn->evict_workers_min > 0);
+        conn->evict_workers_max--;
+        conn->evict_workers_min--;
 
 	return (0);
 }
diff --git a/src/include/connection.h b/src/include/connection.h
index 96c26097045..b07ece5a9aa 100644
--- a/src/include/connection.h
+++ b/src/include/connection.h
@@ -204,6 +204,7 @@ struct __wt_connection_impl {
 	int		 evict_tid_set;	/* Eviction server thread ID set */
 
 	uint32_t	 evict_workers_max;/* Max eviction workers */
+	uint32_t	 evict_workers_min;/* Min eviction workers */
 	uint32_t	 evict_workers;	/* Number of eviction workers */
 	WT_EVICT_WORKER	*evict_workctx;	/* Eviction worker context */
 
diff --git a/src/include/wiredtiger.in b/src/include/wiredtiger.in
index 0b93181e01c..fb04c4743d4 100644
--- a/src/include/wiredtiger.in
+++ b/src/include/wiredtiger.in
@@ -1526,13 +1526,17 @@ struct __wt_connection {
 	 * total memory than the value\, as a percentage of the total cache
 	 * size.  Must be less than \c eviction_trigger., an integer between 10
 	 * and 99; default \c 80.}
+	 * @config{eviction_thread_max, maximum number of threads WiredTiger
+	 * will start to help evict pages from cache.  The number of threads
+	 * currently running will vary depending on the current eviction load.,
+	 * an integer between 1 and 20; default \c 3.}
+	 * @config{eviction_thread_min, minimum number of threads WiredTiger
+	 * will start to help evict pages from cache.  The number of threads
+	 * currently running will vary depending on the current eviction load.,
+	 * an integer between 1 and 20; default \c 1.}
 	 * @config{eviction_trigger, trigger eviction when the cache is using
 	 * this much memory\, as a percentage of the total cache size., an
 	 * integer between 10 and 99; default \c 95.}
-	 * @config{eviction_worker_max, maximum number of additional threads
-	 * WiredTiger will start to help evict pages from cache.  The number of
-	 * threads currently running will vary depending on the current eviction
-	 * load., an integer between 0 and 20; default \c 0.}
 	 * @config{shared_cache = (, shared cache configuration options.  A
 	 * database should configure either a cache_size or a shared_cache not
 	 * both., a set of related configuration options defined below.}
@@ -1842,13 +1846,17 @@ struct __wt_connection {
  * @config{eviction_target, continue evicting until the cache has less total
  * memory than the value\, as a percentage of the total cache size.  Must be
  * less than \c eviction_trigger., an integer between 10 and 99; default \c 80.}
+ * @config{eviction_thread_max, maximum number of threads WiredTiger will start
+ * to help evict pages from cache.  The number of threads currently running will
+ * vary depending on the current eviction load., an integer between 1 and 20;
+ * default \c 3.}
+ * @config{eviction_thread_min, minimum number of threads WiredTiger will start
+ * to help evict pages from cache.  The number of threads currently running will
+ * vary depending on the current eviction load., an integer between 1 and 20;
+ * default \c 1.}
  * @config{eviction_trigger, trigger eviction when the cache is using this much
  * memory\, as a percentage of the total cache size., an integer between 10 and
  * 99; default \c 95.}
- * @config{eviction_worker_max, maximum number of additional threads WiredTiger
- * will start to help evict pages from cache.  The number of threads currently
- * running will vary depending on the current eviction load., an integer between
- * 0 and 20; default \c 0.}
  * @config{exclusive, fail if the database already exists\, generally used with
  * the \c create option., a boolean flag; default \c false.}
  * @config{extensions, list of shared library extensions to load (using dlopen).