improve naming and comments

3 files changed, 29 insertions, 31 deletions

diff --git a/src/main/java/org/traccar/config/Keys.java b/src/main/java/org/traccar/config/Keys.java
index c6a202d2f..a77204175 100644
--- a/src/main/java/org/traccar/config/Keys.java
+++ b/src/main/java/org/traccar/config/Keys.java
@@ -890,11 +890,12 @@ public final class Keys {
             Collections.singletonList(KeyType.GLOBAL));
 
     /**
-     * If FALSE, then filter compares duplicates, distance or period only with the last received location.
-     * Server expects all locations to come sequentially.
+     * If false, the server expects all locations to come sequentially (for each device). Filter checks for duplicates,
+     * distance, speed, or time period only against the location that was last received by server.
      *
-     * If TRUE, then filter compares duplicates, distance or period with Position's fixTime strictly before and after.
-     * Server expects locations to come at random order, since tracking device might go offline.
+     * If true, the server expects locations to come at random order (since tracking device might go offline).
+     * Filter checks for duplicates, distance, speed, or time period against the preceding Position's.
+     * Important: setting to true can cause potential performance issues.
      */
     public static final ConfigKey<Boolean> FILTER_RELATIVE = new ConfigKey<>(
             "filter.relative",
diff --git a/src/main/java/org/traccar/database/DataManager.java b/src/main/java/org/traccar/database/DataManager.java
index 3f702f78a..d8401774e 100644
--- a/src/main/java/org/traccar/database/DataManager.java
+++ b/src/main/java/org/traccar/database/DataManager.java
@@ -340,20 +340,8 @@ public class DataManager {
         }
     }
 
-    public Position getPrevPosition(long deviceId, Date date) throws SQLException {
-        Collection<Position> positions = QueryBuilder.create(dataSource, getQuery("database.selectPrevPosition"))
-                .setLong("deviceId", deviceId)
-                .setDate("time", date)
-                .executeQuery(Position.class);
-        if (positions.isEmpty()) {
-            return null;
-        } else {
-            return positions.iterator().next();
-        }
-    }
-
-    public Position getNextPosition(long deviceId, Date date) throws SQLException {
-        Collection<Position> positions = QueryBuilder.create(dataSource, getQuery("database.selectNextPosition"))
+    public Position getPrecedingPosition(long deviceId, Date date) throws SQLException {
+        Collection<Position> positions = QueryBuilder.create(dataSource, getQuery("database.selectPrecedingPosition"))
                 .setLong("deviceId", deviceId)
                 .setDate("time", date)
                 .executeQuery(Position.class);
diff --git a/src/main/java/org/traccar/handler/FilterHandler.java b/src/main/java/org/traccar/handler/FilterHandler.java
index 16e5ae2da..5287a7639 100644
--- a/src/main/java/org/traccar/handler/FilterHandler.java
+++ b/src/main/java/org/traccar/handler/FilterHandler.java
@@ -146,6 +146,7 @@ public class FilterHandler extends BaseDataHandler {
     }
 
     private boolean filter(Position position) {
+
         if (skipAttributes(position)) {
             return false;
         }
@@ -173,43 +174,44 @@ public class FilterHandler extends BaseDataHandler {
         }
 
         // relative filtering
-        if (filterDuplicate || filterDistance != 0 || filterMaxSpeed != 0 || filterMinPeriod != 0) {
-            Position previous = null;
+        long deviceId = position.getDeviceId();
+        if (filterDuplicate || filterDistance > 0 || filterMaxSpeed > 0 || filterMinPeriod > 0) {
+            Position preceding = null;
             if (filterRelative) {
                 try {
                     Date newFixTime = position.getFixTime();
-                    previous = Context.getDataManager().getPrevPosition(position.getDeviceId(), newFixTime);
+                    preceding = Context.getDataManager().getPrecedingPosition(deviceId, newFixTime);
                 } catch (SQLException e) {
-                    LOGGER.warn("Error filtering position", e);
+                    LOGGER.warn("Error retrieving preceding position; fallbacking to last received position.", e);
+                    preceding = getLastReceivedPosition(deviceId);
                 }
             } else {
-                if (Context.getIdentityManager() != null) {
-                    previous = Context.getIdentityManager().getLastPosition(position.getDeviceId());
-                }
+                preceding = getLastReceivedPosition(deviceId);
             }
-            if (skipLimit(position, previous)) {
+            if (skipLimit(position, preceding)) {
                 return false;
             }
-            if (filterDuplicate(position, previous)) {
+            if (filterDuplicate(position, preceding)) {
                 filterType.append("Duplicate ");
             }
-            if (filterDistance(position, previous)) {
+            if (filterDistance(position, preceding)) {
                 filterType.append("Distance ");
             }
-            if (filterMaxSpeed(position, previous)) {
+            if (filterMaxSpeed(position, preceding)) {
                 filterType.append("MaxSpeed ");
             }
-            if (filterMinPeriod(position, previous)) {
+            if (filterMinPeriod(position, preceding)) {
                 filterType.append("MinPeriod ");
             }
         }
 
         if (filterType.length() > 0) {
+
             StringBuilder message = new StringBuilder();
             message.append("Position filtered by ");
             message.append(filterType.toString());
             message.append("filters from device: ");
-            message.append(Context.getIdentityManager().getById(position.getDeviceId()).getUniqueId());
+            message.append(Context.getIdentityManager().getById(deviceId).getUniqueId());
 
             LOGGER.info(message.toString());
             return true;
@@ -218,6 +220,13 @@ public class FilterHandler extends BaseDataHandler {
         return false;
     }
 
+    private Position getLastReceivedPosition(long deviceId) {
+        if (Context.getIdentityManager() != null) {
+            return Context.getIdentityManager().getLastPosition(deviceId);
+        }
+        return null;
+    }
+
     @Override
     protected Position handlePosition(Position position) {
         if (filter(position)) {