Spreads out backup database saving to avoid lag

https://github.com/BentoBoxWorld/BentoBox/issues/976

src/main/java/world/bentobox/bentobox/BentoBox.java

@@ -184,8 +184,8 @@ public class BentoBox extends JavaPlugin {
 
             // Save islands & players data every X minutes
             instance.getServer().getScheduler().runTaskTimer(instance, () -> {
-                playersManager.saveAll();
-                islandsManager.saveAll();
+                playersManager.asyncSaveAll();
+                islandsManager.asyncSaveAll();
             }, getSettings().getDatabaseBackupPeriod() * 20 * 60L, getSettings().getDatabaseBackupPeriod() * 20 * 60L);
 
             // Make sure all flag listeners are registered.

src/main/java/world/bentobox/bentobox/managers/IslandsManager.java

@@ -5,6 +5,7 @@ import java.util.Collection;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
+import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
@@ -28,6 +29,7 @@ import org.bukkit.entity.Entity;
 import org.bukkit.entity.Player;
 import org.bukkit.entity.PufferFish;
 import org.bukkit.inventory.ItemStack;
+import org.bukkit.scheduler.BukkitTask;
 import org.bukkit.util.Vector;
 import org.eclipse.jdt.annotation.NonNull;
 import org.eclipse.jdt.annotation.Nullable;
@@ -95,6 +97,12 @@ public class IslandsManager {
     @NonNull
     private List<String> deletedIslands;
 
+    private Set<String> toSave = new HashSet<>();
+
+    private Iterator<String> it;
+
+    private BukkitTask task;
+
     /**
      * Islands Manager
      * @param plugin - plugin
@@ -970,6 +978,24 @@ public class IslandsManager {
         }
     }
 
+    /**
+     * Saves all the players at a rate of 1 per tick. Used as a backup.
+     * @since 1.8.0
+     */
+    public void asyncSaveAll() {
+        if (!toSave.isEmpty()) return;
+        // Get a list of ID's to save
+        toSave = islandCache.getAllIslandIds();
+        it = toSave.iterator();
+        task = Bukkit.getScheduler().runTaskTimer(plugin, () -> {
+            if (plugin.isEnabled() && it.hasNext()) {
+                getIslandById(it.next()).ifPresent(this::save);
+            } else {
+               toSave.clear();
+               task.cancel();
+            }
+        }, 0L, 1L);
+    }
     /**
      * Puts a player in a team. Removes them from their old island if required.
      * @param teamIsland - team island

src/main/java/world/bentobox/bentobox/managers/PlayersManager.java

@@ -4,12 +4,15 @@ import java.util.Collection;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
+import java.util.Iterator;
 import java.util.Map;
 import java.util.Set;
 import java.util.UUID;
 
+import org.bukkit.Bukkit;
 import org.bukkit.Location;
 import org.bukkit.World;
+import org.bukkit.scheduler.BukkitTask;
 import org.eclipse.jdt.annotation.NonNull;
 import org.eclipse.jdt.annotation.Nullable;
 
@@ -28,6 +31,9 @@ public class PlayersManager {
 
     private Map<UUID, Players> playerCache;
     private Set<UUID> inTeleport;
+    private Set<UUID> toSave = new HashSet<>();
+    private Iterator<UUID> it;
+    private BukkitTask task;
 
     /**
      * Provides a memory cache of online player information
@@ -69,6 +75,25 @@ public class PlayersManager {
     public void saveAll(){
         Collections.unmodifiableCollection(playerCache.values()).forEach(handler::saveObject);
     }
+    
+    /**
+     * Saves all the players at a rate of 1 per tick. Used as a backup.
+     * @since 1.8.0
+     */
+    public void asyncSaveAll() {
+        if (!toSave.isEmpty()) return;
+        // Get a list of ID's to save
+        toSave = playerCache.keySet();
+        it = toSave.iterator();
+        task = Bukkit.getScheduler().runTaskTimer(plugin, () -> {
+            if (plugin.isEnabled() && it.hasNext()) {
+                this.save(it.next());
+            } else {
+               toSave.clear();
+               task.cancel();
+            }
+        }, 0L, 1L);
+    }
 
     public void shutdown(){
         saveAll();

src/main/java/world/bentobox/bentobox/managers/island/IslandCache.java

@@ -326,4 +326,13 @@ public class IslandCache {
         int setting = BentoBox.getInstance().getIWM().getDefaultIslandFlags(w).getOrDefault(flag, flag.getDefaultRank());
         islandsById.values().stream().filter(i -> i.getWorld().equals(w)).forEach(i -> i.setFlag(flag, setting));
     }
+    
+    /**
+     * Get all the island ids
+     * @return set of ids
+     * @since 1.8.0
+     */
+    public Set<String> getAllIslandIds() {
+        return islandsById.keySet();
+    }
 }