improve log performance by disabling O_SYNC by default (and use fdatasync instead)

src/stasis/flags.c

@@ -64,7 +64,7 @@ char * stasis_store_file_name = "storefile.txt";
 #ifdef STASIS_LOG_FILE_MODE
 int stasis_log_file_mode = STASIS_LOG_FILE_MODE;
 #else
-int stasis_log_file_mode = (O_CREAT | O_RDWR | O_SYNC);
+int stasis_log_file_mode = (O_CREAT | O_RDWR);
 #endif
 
 #ifdef STASIS_LOG_FILE_PERMISSIONS
@@ -74,6 +74,12 @@ int stasis_log_file_permissions = (S_IRUSR | S_IWUSR | S_IRGRP|
                                    S_IWGRP | S_IROTH | S_IWOTH);
 #endif
 
+#ifdef STASIS_LOG_SOFTCOMMIT
+int stasis_log_softcommit = STASIS_LOG_SOFTCOMMIT;
+#else
+int stasis_log_softcommit = 0;
+#endif
+
 #ifdef STASIS_LOG_DIR
 const char* stasis_log_dir_name = STASIS_LOG_DIR;
 #else

src/stasis/logger/safeWrites.c

@@ -409,11 +409,17 @@ static void syncLog_LogWriter(stasis_log_t * log,
   pthread_mutex_unlock(&sw->write_mutex);
 
   fflush(sw->fp);
-  // If we opened the logfile with O_SYNC, fflush() is sufficient.
-  // Otherwise, we're running in soft commit mode and need to manually force
-  // the log before allowing page writeback.
-  if(sw->softcommit && mode == LOG_FORCE_WAL) {
+
+  // We can skip the fsync if we opened with O_SYNC, or if we're in softcommit mode, and not forcing for WAL.
+
+  if(sw->softcommit && mode == LOG_FORCE_WAL  // soft commit mode; syncing for wal
+      || !(sw->softcommit || (sw->filemode & O_SYNC)) // neither soft commit nor opened with O_SYNC
+  ) {
+#ifdef HAVE_FDATASYNC
+  fdatasync(fileno(sw->fp));
+#else
   fsync(fileno(sw->fp));
+#endif
   }
 
   // update flushedLSN after fflush returns.
@@ -749,7 +755,7 @@ static lsn_t firstLogEntry_LogWriter(stasis_log_t* log) {
 }
 
 stasis_log_t* stasis_log_safe_writes_open(const char * filename,
-                                          int filemode, int fileperm) {
+                                          int filemode, int fileperm, int softcommit) {
 
   stasis_log_t proto = {
     sizeofInternalLogEntry_LogWriter, // sizeof_internal_entry
@@ -775,7 +781,7 @@ stasis_log_t* stasis_log_safe_writes_open(const char * filename,
   }
   sw->filemode = filemode;
   sw->fileperm = fileperm;
-  sw->softcommit = !(filemode & O_SYNC);
+  sw->softcommit = softcommit;
 
   stasis_log_t* log = malloc(sizeof(*log));
   memcpy(log,&proto, sizeof(proto));

src/stasis/transactional2.c

@@ -76,7 +76,8 @@ int Tinit() {
   if(LOG_TO_FILE == stasis_log_type) {
     stasis_log_file = stasis_log_safe_writes_open(stasis_log_file_name,
                                                   stasis_log_file_mode,
-                                                  stasis_log_file_permissions);
+                                                  stasis_log_file_permissions,
+                                                  stasis_log_softcommit);
     stasis_log_file->group_force =
       stasis_log_group_force_init(stasis_log_file, 10 * 1000 * 1000); // timeout in nsec; want 10msec.
   } else if(LOG_TO_MEMORY == stasis_log_type) {

stasis/flags.h

@@ -77,6 +77,7 @@ extern int stasis_log_type;
 extern char * stasis_log_file_name;
 extern int    stasis_log_file_mode;
 extern int    stasis_log_file_permissions;
+extern int    stasis_log_softcommit;
 
 extern char * stasis_store_file_name;
 

stasis/logger/safeWrites.h

@@ -56,7 +56,8 @@ BEGIN_C_DECLS
 */
 stasis_log_t* stasis_log_safe_writes_open(const char * filename,
                             int filemode,
-                            int fileperm);
+                            int fileperm,
+                            int softcommit);
 
 /**
   Actually deletes the log file that may have been written to disk! Danger!!

test/stasis/check_logWriter.c

@@ -432,7 +432,8 @@ void reopenLogWorkload(int truncating) {
   if(LOG_TO_FILE == stasis_log_type) {
     stasis_log_file = stasis_log_safe_writes_open(stasis_log_file_name,
                                                   stasis_log_file_mode,
-                                                  stasis_log_file_permissions);
+                                                  stasis_log_file_permissions,
+                                                  stasis_log_softcommit);
   } else if(LOG_TO_MEMORY == stasis_log_type) {
     stasis_log_file = stasis_log_impl_in_memory_open();
   } else {
@@ -465,7 +466,8 @@ void reopenLogWorkload(int truncating) {
   if(LOG_TO_FILE == stasis_log_type) {
     stasis_log_file = stasis_log_safe_writes_open(stasis_log_file_name,
                                                   stasis_log_file_mode,
-                                                  stasis_log_file_permissions);
+                                                  stasis_log_file_permissions,
+                                                  stasis_log_softcommit);
   } else if(LOG_TO_MEMORY == stasis_log_type) {
     stasis_log_file = stasis_log_impl_in_memory_open();
   } else {

utilities/logfile_dump.c

@@ -67,7 +67,8 @@ int main() {
   stasis_log_t* log;
   if(NULL == (log = stasis_log_safe_writes_open(stasis_log_file_name,
                                                 stasis_log_file_mode,
-                                                stasis_log_file_permissions))){
+                                                stasis_log_file_permissions,
+                                                stasis_log_softcommit))){
     printf("Couldn't open log.\n");
   }