在加载器中对大型数据集执行的查询很慢/导致 UI 冻结/卡顿

Question

我有一个查询，它从包含 300,000 个条目的 GPS 位置表中获取 MAX(time)。我有时间索引以及 USER,TIME 索引。

我访问加载器中的位置，每次将新位置插入表时都会收到通知，并将刷新加载器信息从而调用查询

但我的问题是几乎每次发生这种情况时，UI 都会锁定，直到查询完成。

我知道这一点是因为我向提供程序添加了一个 Log.d，以显示每次执行查询需要多少毫秒。有时查询会在 30 毫秒（ish）内执行，但大多数情况下它会花费 2000-4000 毫秒，有时最多需要 6000 毫秒。在此期间，UI 将停止响应。

我有三个问题，

1. 难道不应该使用加载程序来解耦 UI 以这种方式减慢速度，以便长时间查询不会导致 UI 在执行时锁定吗？
2. 是否有任何事情会导致查询等待“锁定”，从而导致它延迟执行，从而使查询花费更长的时间？
3. 为什么查询的执行速度有时看起来变化非常快，但大多数时候却很慢。

我已尝试将提供程序中的查询简化为以下内容，仅用于测试：

queryBuilder = new SQLiteQueryBuilder();
tables = PositionEntry.TABLE_NAME;
queryBuilder.setTables(tables);
projectionMap = new HashMap();
projectionMap.put(PositionEntry.COLUMN_USER, PositionEntry.COLUMN_USER);          
projectionMap.put(PositionEntry.COLUMN_TIME,"MAX("+PositionEntry.COLUMN_TIME + ") AS " +PositionEntry.COLUMN_TIME );
queryBuilder.setProjectionMap(projectionMap);

long start1 = System.currentTimeMillis();
retCursor = queryBuilder.query(mOpenHelper.getReadableDatabase(), null, null, null, PositionEntry.COLUMN_USER, null, null, null);
Log.d(LOG_TAG,"Sub Query took " + (System.currentTimeMillis() - start1) + "ms to complete Rows:" + retCursor.getCount());

我得到了正确的 3 行，并且我根据每个用户的最后一次获得了最后一个位置。但是查询每次执行需要2秒左右。

//编辑：修正了一个代码拼写错误

Answer 1

也许考虑有一个单行表，当将一行插入主表时，通过触发器自动更新最大时间。

假设一个名为 lastentry 的表具有列 lastentry_id（整数，但不是 rowid 的别名）和 lastentry_time（最大时间的整数）并且主表/主表称为 tracker，其中包含 id 列和 time 列（以及其他列）

那么下面

CREATE TRIGGER trg_update_lastentry 
AFTER INSERT ON tracker 
BEGIN  
    UPDATE lastentry 
        SET 
            lastentry_id = new._id, 
            lastentry_time = new.tracker_time 
    WHERE lastentry_time < new.tracker_time
    ; 
END

如果时间在 tracker 表大于 lastnetry 表中的时间。

因此，您无需查询 300,000 行主（跟踪器）表即可提取最大时间。

测试/示例

DBHelper.java :-

public class DBHelper extends SQLiteOpenHelper {

    public static final String DBNAME = "traking";
    public static final int DBVERSION = 1;

    public static final String TB_TRACKER = "tracker";
    public static final String COL_TRACKER_ID = BaseColumns._ID;
    public static final String COL_TRACKER_USER = "tracker_user";
    public static final String COL_TRACKER_TIME = "tracker_time";
    public static final String COL_TRACKER_LATTITUDE = "tracker_lattitude";
    public static final String COL_TRACKER_LONGITUDE = "tracker_longitude";

    public static final String TB_LASTENTRY = "lastentry";
    public static final String COL_LASTENTRY_ID = "lastentry_id";
    public static final String COL_LASTENTRY_TIME = "lastentry_time";

    public static final String TRG_UPDATE_LASTENTRY = "trg_update_lastentry";



    SQLiteDatabase mDB;


    public DBHelper(Context context) {
        super(context, DBNAME, null, DBVERSION);
        mDB = this.getWritableDatabase();
    }

    @Override
    public void onConfigure(SQLiteDatabase db) {
        super.onConfigure(db);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {

        // tracker(main) table
        String crttrackersql = "CREATE TABLE IF NOT EXISTS " + TB_TRACKER +
                "(" +
                COL_TRACKER_ID + " INTEGER PRIMARY KEY," +
                COL_TRACKER_USER + " TEXT," +
                COL_TRACKER_TIME + " INTEGER NOT NULL," +
                COL_TRACKER_LATTITUDE + " INTEGER," +
                COL_TRACKER_LONGITUDE + " INTEGER" +
                ")";
        db.execSQL(crttrackersql);

        // lastentry (max time) table - just has 1 row
        String crtlastentrysql = "CREATE TABLE IF NOT EXISTS " + TB_LASTENTRY +
                "(" +
                COL_LASTENTRY_ID + " INTEGER," +
                COL_LASTENTRY_TIME + " INTEGER" +
                ")";
        db.execSQL(crtlastentrysql);


        //Adds the initial, to be update entry in the lastentry table
        String initlastentry = "INSERT INTO " + TB_LASTENTRY + " VALUES(0,0)";
        db.execSQL(initlastentry);

        //Define the Trigger equivaent of :-
        /*
            CREATE TRIGGER trg_update_lastentry 
            AFTER INSERT ON tracker 
            BEGIN  
                UPDATE lastentry 
                    SET 
                        lastentry_id = new._id, 
                        lastentry_time = new.tracker_time 
                WHERE lastentry_time < new.tracker_time
            ; 
            END

         */
        String crtlastentryupdate = "CREATE TRIGGER IF NOT EXISTS " + TRG_UPDATE_LASTENTRY +
                " AFTER INSERT ON " + TB_TRACKER +
                " BEGIN " +
                " UPDATE " + TB_LASTENTRY +
                " SET " + COL_LASTENTRY_ID + " = new." + COL_TRACKER_ID +
                ", " + COL_LASTENTRY_TIME + " = new." + COL_TRACKER_TIME +
                " WHERE " + COL_LASTENTRY_TIME + " < new." + COL_TRACKER_TIME +
                ";" +
                " END";
        db.execSQL(crtlastentryupdate);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }

    //Used to delete/ redefine the entire Database
    public void restructureDB() {
        String droptracker = "DROP TABLE IF EXISTS " + TB_TRACKER;
        mDB.execSQL(droptracker);
        String droplastentry = "DROp TABLE IF EXISTS " + TB_LASTENTRY;
        mDB.execSQL(droplastentry);
        String droplastentryupdate = "DROP TRIGGER If EXISTS " + TRG_UPDATE_LASTENTRY;
        mDB.execSQL(droplastentryupdate);
        onCreate(mDB);
    }

    //Insert a tracker table entry using current time
    public long insertTracker(String user, long lattitude, long longitude) {
        return insertTrackerWithTime(user,lattitude,longitude, System.currentTimeMillis());
    }

    //Insert a tracker table entry specifying the time
    public long insertTrackerWithTime(String user, long lattitude, long longitude, long time) {
        ContentValues cv = new ContentValues();
        cv.put(COL_TRACKER_TIME, time);
        cv.put(COL_TRACKER_USER,user);
        cv.put(COL_TRACKER_LATTITUDE,lattitude);
        cv.put(COL_TRACKER_LONGITUDE,longitude);
        return mDB.insert(TB_TRACKER,null,cv);
    }
}

MainActivity.java（测试）：-

public class MainActivity extends AppCompatActivity {

    DBHelper mDBHelper; // declare DBHelper

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // Instantiate mDBHelper
        mDBHelper = new DBHelper(this);

        // Insert some rows with various times (noting highest time is not last)
        mDBHelper.insertTracker("Fred",100,100); // NOW
        mDBHelper.insertTrackerWithTime("Bert",110,220,System.currentTimeMillis() - (1000 * 60 * 60 * 24));// Less 1 day
        mDBHelper.insertTrackerWithTime("Bert",110,220,System.currentTimeMillis() - (1000 * 60 * 60 * 24 * 5)); // less 5 days
        mDBHelper.insertTrackerWithTime("Henry",110,220,System.currentTimeMillis() + (1000 * 60 * 60 * 24)); // tomorrow
        mDBHelper.insertTrackerWithTime("Bert",110,220,System.currentTimeMillis() - (1000 * 60 * 60 * 24 * 2)); // less 2 days
        mDBHelper.insertTrackerWithTime("Bert",110,220,System.currentTimeMillis() - (1000 * 60 * 60 * 24 * 7)); // less 1 week

        // get all the inserted rows
        Cursor csr = mDBHelper.getWritableDatabase().query(
                DBHelper.TB_TRACKER,
                null,
                null,
                null,
                null,
                null,
                null
        );
        // Shows the rows in the log
        while (csr.moveToNext()) {
            Log.d("TRACKER",
                    "User = " + csr.getString(csr.getColumnIndex(DBHelper.COL_TRACKER_USER)) +
                            "Time = " + csr.getString(csr.getColumnIndex(DBHelper.COL_TRACKER_TIME))
            );
        }
        // get all the lastentry table rows (1)
        csr = mDBHelper.getWritableDatabase().query(
                DBHelper.TB_LASTENTRY,
                null,
                null,
                null,
                null,
                null,
                null
        );
        // log the values
        while (csr.moveToNext()) {
            Log.d("MAXTIME", "Maximum Time is " + csr.getString(csr.getColumnIndex(DBHelper.COL_LASTENTRY_TIME)) +
                    " for ID = " + csr.getString(csr.getColumnIndex(DBHelper.COL_LASTENTRY_ID))
            );
        }
    }
}

结果：-

04-19 00:44:17.037 1645-1645/? D/TRACKER: User = FredTime = 1524098657028
    User = BertTime = 1524012257031
04-19 00:44:17.041 1645-1645/? D/TRACKER: User = BertTime = 1523666657033
    User = HenryTime = 1524185057036
    User = BertTime = 1523925857039
    User = BertTime = 1523493857041
04-19 00:44:17.041 1645-1645/? D/MAXTIME: Maximum Time is 1524185057036 for ID = 4

即最大时间为 1524185057036，它反映了 6 行中的第 4 行。