Addresses #2168 refs[t:2168] Skip fsync for transactions that have done no (modify) work.

i.e. only queries

git-svn-id: file:///svn/toku/tokudb.2037b@15766 c7de825b-a66e-492c-adef-691d508d4ae1

newbrt/brt.c

@@ -2632,10 +2632,17 @@ int toku_brt_insert (BRT brt, DBT *key, DBT *val, TOKUTXN txn) {
     return toku_brt_maybe_insert(brt, key, val, txn, FALSE, ZERO_LSN);
 }
 
+static void
+txn_note_doing_work(TOKUTXN txn) {
+    if (txn)
+        txn->has_done_work = 1;
+}
+
 int toku_brt_maybe_insert (BRT brt, DBT *key, DBT *val, TOKUTXN txn, BOOL oplsn_valid, LSN oplsn) {
     int r = 0;
     XIDS message_xids;
     TXNID xid = toku_txn_get_txnid(txn);
+    txn_note_doing_work(txn);
     if (txn && (brt->h->txnid_that_created_or_locked_when_empty != xid)) {
         BYTESTRING keybs  = {key->size, toku_memdup_in_rollback(txn, key->data, key->size)};
         int need_data = (brt->flags&TOKU_DB_DUPSORT)!=0; // dupsorts don't need the data part
@@ -2681,6 +2688,7 @@ int toku_brt_maybe_delete(BRT brt, DBT *key, TOKUTXN txn, BOOL oplsn_valid, LSN
     int r;
     XIDS message_xids;
     TXNID xid = toku_txn_get_txnid(txn);
+    txn_note_doing_work(txn);
     if (txn && (brt->h->txnid_that_created_or_locked_when_empty != xid)) {
         BYTESTRING keybs  = {key->size, toku_memdup_in_rollback(txn, key->data, key->size)};
         r = toku_logger_save_rollback_cmddelete(txn, toku_cachefile_filenum(brt->cf), keybs);
@@ -4774,6 +4782,7 @@ int toku_brt_maybe_delete_both(BRT brt, DBT *key, DBT *val, TOKUTXN txn, BOOL op
     int r;
     XIDS message_xids;
     TXNID xid = toku_txn_get_txnid(txn);
+    txn_note_doing_work(txn);
     if (txn && (brt->h->txnid_that_created_or_locked_when_empty != xid)) {
         BYTESTRING keybs  = {key->size, toku_memdup_in_rollback(txn, key->data, key->size)};
         BYTESTRING databs = {val->size, toku_memdup_in_rollback(txn, val->data, val->size)};

newbrt/log-internal.h

@@ -119,6 +119,7 @@ struct tokutxn {
     OMT        open_brts; // a collection of the brts that we touched.  Indexed by filenum.
     XIDS       xids;      //Represents the xid list
     int        force_fsync_on_commit;  //This transaction NEEDS an fsync once (if) it commits.  (commit means root txn)
+    int        has_done_work;          //If this transaction has not done work, there is no need to fsync.
 };
 
 static inline int toku_logsizeof_u_int8_t (u_int32_t v __attribute__((__unused__))) {

newbrt/rollback.c

@@ -155,6 +155,7 @@ int toku_rollback_commit(TOKUTXN txn, YIELDF yield, void*yieldv, LSN lsn) {
         //If this transaction needs an fsync (if it commits)
         //save that in the parent.  Since the commit really happens in the root txn.
         txn->parent->force_fsync_on_commit |= txn->force_fsync_on_commit;
+        txn->parent->has_done_work         |= txn->has_done_work;
     } else {
         // do the commit calls and free everything
         // we do the commit calls in reverse order too.

newbrt/txn.c

@@ -61,6 +61,7 @@ int toku_txn_begin_with_xid (TOKUTXN parent_tokutxn, TOKUTXN *tokutxn, TOKULOGGE
     result->rollentry_fd = -1;
     result->rollentry_filesize = 0;
     result->force_fsync_on_commit = 0;
+    result->has_done_work = 0;
     *tokutxn = result;
     return 0;
 
@@ -81,7 +82,8 @@ int toku_txn_commit_with_lsn(TOKUTXN txn, int nosync, YIELDF yield, void *yieldv
     // panic handled in log_commit
 
     //Child transactions do not actually 'commit'.  They promote their changes to parent, so no need to fsync if this txn has a parent.
-    int do_fsync = !txn->parent && (txn->force_fsync_on_commit || !nosync);
+    int do_fsync = !txn->parent && (txn->force_fsync_on_commit || (!nosync && txn->has_done_work));
+
     r = toku_log_commit(txn->logger, (LSN*)0, do_fsync, txn->txnid64); // exits holding neither of the tokulogger locks.
     if (r!=0)
         return r;