From 83cb935e4cb7e0bd4bb2dfbd72199e689518e45e Mon Sep 17 00:00:00 2001
From: Anton Tananaev <anton@traccar.org>
Date: Fri, 10 Jul 2026 19:37:55 -0700
Subject: [PATCH] Enable database result streaming

---
 src/main/java/org/traccar/config/Keys.java    | 11 +++++++++-
 .../org/traccar/storage/DatabaseStorage.java  |  2 +-
 .../org/traccar/storage/QueryBuilder.java     | 21 +++++++++++++++++--
 .../org/traccar/storage/QueryBuilderTest.java |  6 +++---
 4 files changed, 33 insertions(+), 7 deletions(-)

diff --git a/src/main/java/org/traccar/config/Keys.java b/src/main/java/org/traccar/config/Keys.java
index d2fe05e20..a7ed0e865 100644
--- a/src/main/java/org/traccar/config/Keys.java
+++ b/src/main/java/org/traccar/config/Keys.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2019 - 2025 Anton Tananaev (anton@traccar.org)
+ * Copyright 2019 - 2026 Anton Tananaev (anton@traccar.org)
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -579,6 +579,15 @@ public final class Keys {
             List.of(KeyType.CONFIG),
             20);
 
+    /**
+     * Number of rows fetched per round trip for streamed queries (position history and exports). On PostgreSQL this
+     * enables a server-side cursor so results are not fully buffered in memory.
+     */
+    public static final ConfigKey<Integer> DATABASE_STREAM_FETCH_SIZE = new IntegerConfigKey(
+            "database.streamFetchSize",
+            List.of(KeyType.CONFIG),
+            1000);
+
     /**
      * SQL query to check connection status. Default value is 'SELECT 1'. For Oracle database you can use
      * 'SELECT 1 FROM DUAL'.
diff --git a/src/main/java/org/traccar/storage/DatabaseStorage.java b/src/main/java/org/traccar/storage/DatabaseStorage.java
index b08d413ec..381060dbd 100644
--- a/src/main/java/org/traccar/storage/DatabaseStorage.java
+++ b/src/main/java/org/traccar/storage/DatabaseStorage.java
@@ -86,7 +86,7 @@ public class DatabaseStorage extends Storage {
             for (int index = 0; index < values.size(); index++) {
                 builder.setValue(index, values.get(index));
             }
-            Stream<T> stream = builder.executeQueryStreamed(clazz);
+            Stream<T> stream = builder.executeQueryStreamed(clazz, databaseType);
             builder = null;
             return stream;
         } catch (SQLException e) {
diff --git a/src/main/java/org/traccar/storage/QueryBuilder.java b/src/main/java/org/traccar/storage/QueryBuilder.java
index 15006e2d0..c23eff783 100644
--- a/src/main/java/org/traccar/storage/QueryBuilder.java
+++ b/src/main/java/org/traccar/storage/QueryBuilder.java
@@ -59,6 +59,8 @@ public final class QueryBuilder implements AutoCloseable {
     private final String query;
     private final boolean returnGeneratedKeys;
 
+    private boolean streamingTransaction;
+
     private QueryBuilder(
             Config config, DataSource dataSource, ObjectMapper objectMapper,
             String query, boolean returnGeneratedKeys) throws SQLException {
@@ -234,11 +236,18 @@ public final class QueryBuilder implements AutoCloseable {
         }
     }
 
-    public <T> Stream<T> executeQueryStreamed(Class<T> clazz) throws SQLException {
+    public <T> Stream<T> executeQueryStreamed(Class<T> clazz, String databaseType) throws SQLException {
         ResultSet resultSet = null;
         try {
             logQuery();
 
+            connection.setAutoCommit(false);
+            streamingTransaction = true;
+            statement.setFetchSize(switch (databaseType) {
+                case "MySQL", "MariaDB" -> Integer.MIN_VALUE;
+                default -> config.getInteger(Keys.DATABASE_STREAM_FETCH_SIZE);
+            });
+
             resultSet = statement.executeQuery();
             ResultSetMetaData resultMetaData = resultSet.getMetaData();
 
@@ -311,7 +320,15 @@ public final class QueryBuilder implements AutoCloseable {
         try {
             statement.close();
         } finally {
-            connection.close();
+            try {
+                if (streamingTransaction) {
+                    streamingTransaction = false;
+                    connection.rollback();
+                    connection.setAutoCommit(true);
+                }
+            } finally {
+                connection.close();
+            }
         }
     }
 
diff --git a/src/test/java/org/traccar/storage/QueryBuilderTest.java b/src/test/java/org/traccar/storage/QueryBuilderTest.java
index e01935560..4ea136ff6 100644
--- a/src/test/java/org/traccar/storage/QueryBuilderTest.java
+++ b/src/test/java/org/traccar/storage/QueryBuilderTest.java
@@ -96,7 +96,7 @@ public class QueryBuilderTest {
 
         try (QueryBuilder query = QueryBuilder.create(config, dataSource, objectMapper,
                 "SELECT * FROM test_entity");
-             Stream<TestEntity> stream = query.executeQueryStreamed(TestEntity.class)) {
+             Stream<TestEntity> stream = query.executeQueryStreamed(TestEntity.class, "H2")) {
             List<TestEntity> results = stream.toList();
             assertEquals(1, results.size());
             TestEntity entity = results.get(0);
@@ -132,7 +132,7 @@ public class QueryBuilderTest {
 
         try (QueryBuilder query = QueryBuilder.create(config, dataSource, objectMapper,
                 "SELECT * FROM test_entity");
-             Stream<TestEntity> stream = query.executeQueryStreamed(TestEntity.class)) {
+             Stream<TestEntity> stream = query.executeQueryStreamed(TestEntity.class, "H2")) {
             List<TestEntity> results = stream.toList();
             assertEquals(1, results.size());
             TestEntity loaded = results.get(0);
@@ -161,7 +161,7 @@ public class QueryBuilderTest {
 
         try (QueryBuilder query = QueryBuilder.create(config, dataSource, objectMapper,
                 "SELECT * FROM test_entity ORDER BY count");
-             Stream<TestEntity> stream = query.executeQueryStreamed(TestEntity.class)) {
+             Stream<TestEntity> stream = query.executeQueryStreamed(TestEntity.class, "H2")) {
             List<TestEntity> results = stream.toList();
             assertEquals(3, results.size());
             assertEquals("row0", results.get(0).getName());