Inefficient Usages of Java Collections

core/src/main/java/cn/edu/tsinghua/iginx/cluster/IginxWorker.java

@@ -62,7 +62,7 @@
 
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
-import java.util.ArrayList;
+import java.util.LinkedList;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -178,7 +178,7 @@ public Status addStorageEngines(AddStorageEnginesReq req) {
             return RpcUtils.ACCESS_DENY;
         }
         List<StorageEngine> storageEngines = req.getStorageEngines();
-        List<StorageEngineMeta> storageEngineMetas = new ArrayList<>();
+        LinkedList<StorageEngineMeta> storageEngineMetas = new LinkedList<>();
 
         Map<cn.edu.tsinghua.iginx.db.StorageEngine, Method> checkConnectionMethods = new HashMap<>();
         String[] driverInfos = ConfigDescriptor.getInstance().getConfig().getDatabaseClassNames().split(",");
@@ -219,7 +219,7 @@ public Status addStorageEngines(AddStorageEnginesReq req) {
         Status status = RpcUtils.SUCCESS;
         // 检测是否与已有的存储单元冲突
         List<StorageEngineMeta> currentStorageEngines = metaManager.getStorageEngineList();
-        List<StorageEngineMeta> duplicatedStorageEngine = new ArrayList<>();
+        List<StorageEngineMeta> duplicatedStorageEngine = new LinkedList<>();
         for (StorageEngineMeta storageEngine: storageEngineMetas) {
             for (StorageEngineMeta currentStorageEngine: currentStorageEngines) {
                 if (currentStorageEngine.getIp().equals(storageEngine.getIp()) && currentStorageEngine.getPort() == storageEngine.getPort()) {
@@ -238,7 +238,7 @@ public Status addStorageEngines(AddStorageEnginesReq req) {
             status.setMessage("unexpected repeated add");
         }
         if (!storageEngineMetas.isEmpty()) {
-            storageEngineMetas.get(storageEngineMetas.size() - 1).setLastOfBatch(true); // 每一批最后一个是 true，表示需要进行扩容
+            storageEngineMetas.getLast().setLastOfBatch(true); // 每一批最后一个是 true，表示需要进行扩容
         }
         if (!metaManager.addStorageEngines(storageEngineMetas)) {
             status = RpcUtils.FAILURE;

core/src/main/java/cn/edu/tsinghua/iginx/metadata/DefaultMetaManager.java

@@ -42,6 +42,7 @@
 import org.slf4j.LoggerFactory;
 
 import java.util.ArrayList;
+import java.util.LinkedList;
 import java.util.Collections;
 import java.util.Comparator;
 import java.util.HashMap;
@@ -105,7 +106,7 @@ private DefaultMetaManager() {
                 break;
         }
 
-        storageEngineChangeHooks = Collections.synchronizedList(new ArrayList<>());
+        storageEngineChangeHooks = Collections.synchronizedList(new LinkedList<>());
 
         try {
             initIginx();

core/src/main/java/cn/edu/tsinghua/iginx/query/expression/BooleanExpression.java

@@ -20,6 +20,7 @@
 
 import java.util.ArrayDeque;
 import java.util.ArrayList;
+import java.util.LinkedList;
 import java.util.Deque;
 import java.util.List;
 import java.util.Map;
@@ -28,7 +29,7 @@ public class BooleanExpression {
     private String boolExpression;
     private List<Element> postfixExpression;
     private TreeNode root;
-    private List<String> timeseries = new ArrayList<>();
+    private List<String> timeseries = new LinkedList<>();
 
     public BooleanExpression(String str) {
         boolExpression = str;

core/src/main/java/cn/edu/tsinghua/iginx/rest/insert/DataPointsParser.java

@@ -33,6 +33,7 @@
 
 import java.io.Reader;
 import java.util.ArrayList;
+import java.util.LinkedList;
 import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
@@ -46,7 +47,7 @@ public class DataPointsParser {
     private final IMetaManager metaManager = DefaultMetaManager.getInstance();
     private Reader inputStream = null;
     private ObjectMapper mapper = new ObjectMapper();
-    private List<Metric> metricList = new ArrayList<>();
+    private List<Metric> metricList = new LinkedList<>();
     private RestSession session = new RestSession();
 
     public DataPointsParser() {
@@ -347,4 +348,4 @@ DataType findType(List<String> values) {
         }
         return DataType.DOUBLE;
     }
-}
+}

core/src/main/java/cn/edu/tsinghua/iginx/rest/query/QueryMetric.java

@@ -21,6 +21,7 @@
 import cn.edu.tsinghua.iginx.rest.query.aggregator.QueryAggregator;
 
 import java.util.ArrayList;
+import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
 import java.util.TreeMap;
@@ -29,7 +30,7 @@ public class QueryMetric {
     private String name;
     private Long limit;
     private Map<String, List<String>> tags = new TreeMap();
-    private List<QueryAggregator> aggregators = new ArrayList<>();
+    private List<QueryAggregator> aggregators = new LinkedList<>();
     private Boolean annotation = false;
     private AnnotationLimit annotationLimit;
 

core/src/main/java/cn/edu/tsinghua/iginx/rest/query/QueryResult.java

@@ -262,7 +262,7 @@ private String sampleSizeToString(int num) {
     private Map<String, List<String>> getTagsFromPaths(String name, List<String> paths) throws Exception {
         List<Map<String, Integer>> dup = new ArrayList<>();
         Map<String, List<String>> ret = new TreeMap<>();
-        Map<Integer, String> pos2path = new TreeMap<>();
+        Map<Integer, String> pos2path = new HashMap<>();
         Map<String, Integer> metricschema = metaManager.getSchemaMapping(name);
         if (metricschema == null) {
             throw new Exception("No metadata found");

core/src/main/java/cn/edu/tsinghua/iginx/rest/query/aggregator/QueryAggregatorSaveAs.java

@@ -25,6 +25,7 @@
 import cn.edu.tsinghua.iginx.session.SessionQueryDataSet;
 
 import java.util.ArrayList;
+import java.util.LinkedList;
 import java.util.List;
 
 public class QueryAggregatorSaveAs extends QueryAggregator {
@@ -35,7 +36,7 @@ public QueryAggregatorSaveAs() {
     @Override
     public QueryResultDataset doAggregate(RestSession session, List<String> paths, long startTimestamp, long endTimestamp) {
         DataPointsParser parser = new DataPointsParser();
-        List<Metric> metrics = new ArrayList<>();
+        List<Metric> metrics = new LinkedList<>();
         Metric ins = new Metric();
         String name = paths.get(0).split("\\.")[paths.get(0).split("\\.").length - 1];
         ins.setName(getMetric_name());

core/src/main/java/cn/edu/tsinghua/iginx/sql/operator/SelectOperator.java

@@ -16,6 +16,7 @@
 import cn.edu.tsinghua.iginx.utils.RpcUtils;
 
 import java.util.ArrayList;
+import java.util.LinkedList;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
@@ -41,7 +42,7 @@ public class SelectOperator extends Operator {
     public SelectOperator() {
         this.operatorType = OperatorType.SELECT;
         this.queryType = QueryType.Unknown;
-        selectedFuncsAndPaths = new ArrayList<>();
+        selectedFuncsAndPaths = new LinkedList<>();
         funcTypeSet = new HashSet<>();
         fromPath = "";
         startTime = Long.MIN_VALUE;

jdbc/src/main/java/cn/edu/tsinghua/iginx/jdbc/IginXPreparedStatement.java

@@ -13,7 +13,7 @@
 public class IginXPreparedStatement extends IginXStatement implements PreparedStatement {
 
     private String sql;
-    private final Map<Integer, String> params = new LinkedHashMap<>();
+    private final Map<Integer, String> params = new HashMap<>();
 
     public IginXPreparedStatement(IginXConnection connection, Session session, String sql) {
         super(connection, session);

session/src/main/java/cn/edu/tsinghua/iginx/session/LastQueryDataSet.java

@@ -22,6 +22,7 @@
 import cn.edu.tsinghua.iginx.thrift.LastQueryResp;
 
 import java.util.ArrayList;
+import java.util.LinkedList;
 import java.util.List;
 
 import static cn.edu.tsinghua.iginx.utils.ByteUtils.getLongArrayFromByteBuffer;
@@ -36,7 +37,7 @@ public class LastQueryDataSet {
     }
 
     LastQueryDataSet(LastQueryResp resp) {
-        points = new ArrayList<>();
+        points = new LinkedList<>();
         List<String> paths = resp.getPaths();
         List<DataType> dataTypes = resp.getDataTypeList();
         long[] timestamps = getLongArrayFromByteBuffer(resp.timestamps);