mdbx: rework env_sync() for MDBX_NOMETASYNC, add mdbx_env_sync_poll().

Change-Id: I4d212c663853b00e221d17cb8483353231497b48

mdbx.h

@@ -1614,8 +1614,11 @@ LIBMDBX_API int mdbx_env_info(MDBX_env *env, MDBX_envinfo *info, size_t bytes);
  * provide polling mode for lazy/asynchronous sync in conjunction with
  * mdbx_env_set_syncbytes() and/or mdbx_env_set_syncperiod().
  *
- * Legacy mdbx_env_sync() correspond to calling mdbx_env_sync_ex() with the
+ * The mdbx_env_sync() is shortcut to calling mdbx_env_sync_ex() with
- * argument nonblock=false.
+ * try force=true and nonblock=false arguments.
+ *
+ * The mdbx_env_sync_poll() is shortcut to calling mdbx_env_sync_ex() with
+ * the force=false and nonblock=true arguments.
  *
  * NOTE: This call is not valid if the environment was opened with MDBX_RDONLY.
  *
@@ -1628,13 +1631,15 @@ LIBMDBX_API int mdbx_env_info(MDBX_env *env, MDBX_envinfo *info, size_t bytes);
  * [in] nonblock  Don't wait if write transaction is running by other thread.
  *
  * Returns A non-zero error value on failure and MDBX_RESULT_TRUE or 0 on
- * success. The MDBX_RESULT_TRUE means some data was flushed to disk,
+ * success. The MDBX_RESULT_TRUE means no data pending for flush to disk,
  * and 0 otherwise. Some possible errors are:
  *  - MDBX_EACCES   = the environment is read-only.
+ *  - MDBX_BUSY     = the environment is used by other thread and nonblock=true.
  *  - MDBX_EINVAL   = an invalid parameter was specified.
  *  - MDBX_EIO      = an error occurred during synchronization. */
 LIBMDBX_API int mdbx_env_sync_ex(MDBX_env *env, int force, int nonblock);
-LIBMDBX_API int mdbx_env_sync(MDBX_env *env, int force);
+LIBMDBX_API int mdbx_env_sync(MDBX_env *env);
+LIBMDBX_API int mdbx_env_sync_poll(MDBX_env *env);
 
 /* Sets threshold to force flush the data buffers to disk,
  * even of MDBX_NOSYNC, MDBX_NOMETASYNC and MDBX_MAPASYNC flags
@@ -1649,12 +1654,12 @@ LIBMDBX_API int mdbx_env_sync(MDBX_env *env, int force);
  * The default is 0, than mean no any threshold checked, and no additional
  * flush will be made.
  *
- * [in] env     An environment handle returned by mdbx_env_create()
+ * [in] env         An environment handle returned by mdbx_env_create().
- * [in] bytes   The size in bytes of summary changes when a synchronous
+ * [in] threshold   The size in bytes of summary changes when a synchronous
- *              flush would be made.
+ *                  flush would be made.
  *
  * Returns A non-zero error value on failure and 0 on success. */
-LIBMDBX_API int mdbx_env_set_syncbytes(MDBX_env *env, size_t bytes);
+LIBMDBX_API int mdbx_env_set_syncbytes(MDBX_env *env, size_t threshold);
 
 /* Sets relative period since the last unsteay commit to force flush the data
  * buffers to disk, even of MDBX_NOSYNC, MDBX_NOMETASYNC and MDBX_MAPASYNC flags

src/elements/core.c

@@ -2561,13 +2561,35 @@ static __hot MDBX_meta *mdbx_meta_head(const MDBX_env *env) {
   return mdbx_meta_mostrecent(prefer_last, env);
 }
 
+static __hot txnid_t mdbx_recent_committed_txnid(const MDBX_env *env) {
+  while (true) {
+    const MDBX_meta *head = mdbx_meta_head(env);
+    const txnid_t recent = mdbx_meta_txnid_fluid(env, head);
+    mdbx_compiler_barrier();
+    if (likely(head == mdbx_meta_head(env) &&
+               recent == mdbx_meta_txnid_fluid(env, head)))
+      return recent;
+  }
+}
+
+static __hot txnid_t mdbx_recent_steady_txnid(const MDBX_env *env) {
+  while (true) {
+    const MDBX_meta *head = mdbx_meta_steady(env);
+    const txnid_t recent = mdbx_meta_txnid_fluid(env, head);
+    mdbx_compiler_barrier();
+    if (likely(head == mdbx_meta_steady(env) &&
+               recent == mdbx_meta_txnid_fluid(env, head)))
+      return recent;
+  }
+}
+
 static __hot txnid_t mdbx_reclaiming_detent(const MDBX_env *env) {
   if (F_ISSET(env->me_flags, MDBX_UTTERLY_NOSYNC))
     return likely(env->me_txn0->mt_owner == mdbx_thread_self())
                ? env->me_txn0->mt_txnid - 1
-               : mdbx_meta_txnid_fluid(env, mdbx_meta_head(env));
+               : mdbx_recent_committed_txnid(env);
 
-  return mdbx_meta_txnid_stable(env, mdbx_meta_steady(env));
+  return mdbx_recent_steady_txnid(env);
 }
 
 static const char *mdbx_durable_str(const MDBX_meta *const meta) {
@@ -3435,16 +3457,22 @@ __cold int mdbx_env_sync_ex(MDBX_env *env, int force, int nonblock) {
   if (unlikely(flags & (MDBX_RDONLY | MDBX_FATAL_ERROR)))
     return MDBX_EACCESS;
 
-  const bool outside_txn =
+  if (unlikely(!env->me_map))
-      (!env->me_txn0 || env->me_txn0->mt_owner != mdbx_thread_self());
+    return MDBX_EPERM;
 
+  int rc = MDBX_RESULT_TRUE /* means "nothing to sync" */;
+  bool need_unlock = false;
+  if (nonblock && *env->me_unsynced_pages == 0)
+    goto fastpath;
+
+  const bool outside_txn = (env->me_txn0->mt_owner != mdbx_thread_self());
   if (outside_txn) {
     int err = mdbx_txn_lock(env, nonblock);
     if (unlikely(err != MDBX_SUCCESS))
       return err;
+    need_unlock = true;
   }
 
-  int rc = MDBX_RESULT_FALSE /* means "nothing to sync" */;
   const MDBX_meta *head = mdbx_meta_head(env);
   pgno_t unsynced_pages = *env->me_unsynced_pages;
   if (!META_IS_STEADY(head) || unsynced_pages) {
@@ -3479,7 +3507,7 @@ __cold int mdbx_env_sync_ex(MDBX_env *env, int force, int nonblock) {
       }
       env->me_txn0->mt_txnid = meta_txnid(env, head, false);
       mdbx_find_oldest(env->me_txn0);
-      rc = MDBX_RESULT_TRUE /* means "some data was synced" */;
+      rc = MDBX_RESULT_FALSE /* means "some data was synced" */;
     }
 
     if (!META_IS_STEADY(head) ||
@@ -3490,28 +3518,39 @@ __cold int mdbx_env_sync_ex(MDBX_env *env, int force, int nonblock) {
       MDBX_meta meta = *head;
       int err = mdbx_sync_locked(env, flags | MDBX_SHRINK_ALLOWED, &meta);
       if (unlikely(err != MDBX_SUCCESS)) {
-        if (outside_txn)
+        if (need_unlock)
           mdbx_txn_unlock(env);
         return err;
       }
-      rc = MDBX_RESULT_TRUE /* means "some data was synced" */;
+      rc = MDBX_RESULT_FALSE /* means "some data was synced" */;
     }
   }
 
+fastpath:
   /* LY: sync meta-pages if MDBX_NOMETASYNC enabled
    *     and someone was not synced above. */
-  if (rc == MDBX_RESULT_FALSE && (env->me_flags & MDBX_NOMETASYNC) != 0)
+  if (rc == MDBX_RESULT_TRUE && (env->me_flags & MDBX_NOMETASYNC) != 0) {
-    rc = (flags & MDBX_WRITEMAP)
+    const txnid_t head_txnid = mdbx_recent_committed_txnid(env);
-             ? mdbx_msync(&env->me_dxb_mmap, 0, pgno2bytes(env, NUM_METAS),
+    if (*env->me_meta_sync_txnid != (uint32_t)head_txnid) {
-                          false)
+      rc = (flags & MDBX_WRITEMAP)
-             : mdbx_filesync(env->me_fd, MDBX_SYNC_DATA | MDBX_SYNC_IODQ);
+               ? mdbx_msync(&env->me_dxb_mmap, 0, pgno2bytes(env, NUM_METAS),
-  if (outside_txn)
+                            false)
+               : mdbx_filesync(env->me_fd, MDBX_SYNC_DATA | MDBX_SYNC_IODQ);
+      if (likely(rc == MDBX_SUCCESS))
+        *env->me_meta_sync_txnid = (uint32_t)head_txnid;
+    }
+  }
+  if (need_unlock)
     mdbx_txn_unlock(env);
   return rc;
 }
 
-__cold int mdbx_env_sync(MDBX_env *env, int force) {
+__cold int mdbx_env_sync(MDBX_env *env) {
-  return mdbx_env_sync_ex(env, force, false);
+  return mdbx_env_sync_ex(env, true, false);
+}
+
+__cold int mdbx_env_sync_poll(MDBX_env *env) {
+  return mdbx_env_sync_ex(env, false, true);
 }
 
 /* Back up parent txn's cursors, then grab the originals for tracking */
@@ -6184,6 +6223,7 @@ static int mdbx_sync_locked(MDBX_env *env, unsigned flags,
       if (rc != MDBX_SUCCESS)
         goto undo;
     }
+    *env->me_meta_sync_txnid = (uint32_t)pending->mm_txnid_a.inconsistent;
   }
 
   /* LY: shrink datafile if needed */
@@ -7127,6 +7167,7 @@ static int __cold mdbx_setup_lck(MDBX_env *env, char *lck_pathname,
     env->me_unsynced_pages = &env->me_lckless_stub.autosync_pending;
     env->me_autosync_threshold = &env->me_lckless_stub.autosync_threshold;
     env->me_discarded_tail = &env->me_lckless_stub.discarded_tail;
+    env->me_meta_sync_txnid = &env->me_lckless_stub.meta_sync_txnid;
     env->me_maxreaders = UINT_MAX;
 #ifdef MDBX_OSAL_LOCK
     env->me_wmutex = &env->me_lckless_stub.wmutex;
@@ -7278,6 +7319,7 @@ static int __cold mdbx_setup_lck(MDBX_env *env, char *lck_pathname,
   env->me_unsynced_pages = &env->me_lck->mti_unsynced_pages;
   env->me_autosync_threshold = &env->me_lck->mti_autosync_threshold;
   env->me_discarded_tail = &env->me_lck->mti_discarded_tail;
+  env->me_meta_sync_txnid = &env->me_lck->mti_meta_sync_txnid;
 #ifdef MDBX_OSAL_LOCK
   env->me_wmutex = &env->me_lck->mti_wmutex;
 #endif
@@ -13938,7 +13980,7 @@ static txnid_t __cold mdbx_oomkick(MDBX_env *env, const txnid_t laggard) {
   return mdbx_find_oldest(env->me_txn);
 }
 
-int __cold mdbx_env_set_syncbytes(MDBX_env *env, size_t bytes) {
+int __cold mdbx_env_set_syncbytes(MDBX_env *env, size_t threshold) {
   if (unlikely(!env))
     return MDBX_EINVAL;
 
@@ -13951,8 +13993,13 @@ int __cold mdbx_env_set_syncbytes(MDBX_env *env, size_t bytes) {
   if (unlikely(!env->me_map))
     return MDBX_EPERM;
 
-  *env->me_autosync_threshold = bytes2pgno(env, bytes + env->me_psize - 1);
+  *env->me_autosync_threshold = bytes2pgno(env, threshold + env->me_psize - 1);
-  return bytes ? mdbx_env_sync(env, false) : MDBX_SUCCESS;
+  if (threshold) {
+    int err = mdbx_env_sync_poll(env);
+    if (unlikely(MDBX_IS_ERROR(err)))
+      return err;
+  }
+  return MDBX_SUCCESS;
 }
 
 int __cold mdbx_env_set_syncperiod(MDBX_env *env, unsigned seconds_16dot16) {
@@ -13969,7 +14016,12 @@ int __cold mdbx_env_set_syncperiod(MDBX_env *env, unsigned seconds_16dot16) {
     return MDBX_EPERM;
 
   *env->me_autosync_period = mdbx_osal_16dot16_to_monotime(seconds_16dot16);
-  return seconds_16dot16 ? mdbx_env_sync(env, false) : MDBX_SUCCESS;
+  if (seconds_16dot16) {
+    int err = mdbx_env_sync_poll(env);
+    if (unlikely(MDBX_IS_ERROR(err)))
+      return err;
+  }
+  return MDBX_SUCCESS;
 }
 
 int __cold mdbx_env_set_oomfunc(MDBX_env *env, MDBX_oom_func *oomfunc) {

src/elements/internals.h

@@ -521,7 +521,9 @@ typedef struct MDBX_lockinfo {
    * zero means no-threshold, i.e. auto-sync is disabled. */
   volatile pgno_t mti_autosync_threshold;
 
-  uint32_t reserved_pad;
+  /* Low 32-bit of txnid with which meta-pages was synced,
+   * i.e. for sync-polling in the MDBX_NOMETASYNC mode. */
+  volatile uint32_t mti_meta_sync_txnid;
 
   /* Period for timed auto-sync feature, i.e. at the every steady checkpoint
    * the mti_unsynced_timeout sets to the current_time + mti_autosync_period.
@@ -938,6 +940,7 @@ struct MDBX_env {
   volatile pgno_t *me_unsynced_pages;
   volatile pgno_t *me_autosync_threshold;
   volatile pgno_t *me_discarded_tail;
+  volatile uint32_t *me_meta_sync_txnid;
   MDBX_oom_func *me_oom_func; /* Callback for kicking laggard readers */
   struct {
 #ifdef MDBX_OSAL_LOCK
@@ -949,6 +952,7 @@ struct MDBX_env {
     pgno_t autosync_pending;
     pgno_t autosync_threshold;
     pgno_t discarded_tail;
+    uint32_t meta_sync_txnid;
   } me_lckless_stub;
 #if MDBX_DEBUG
   MDBX_assert_func *me_assert_func; /*  Callback for assertion failures */