快速读取使用simpleQueryForBlobFileDescriptor内SQLite的斑点？ [英] fast read of blobs within SQLite using simpleQueryForBlobFileDescriptor?

问题描述

我用下面的code读斑点与SQLite的在我的Andr​​oid应用100KB和1000KB的大小：

 公共对象getCachefromDb（字符串sIdentifier）{    字符串sSQL ='+ sIdentifier +选择从cachtable其中identifier =缓存';    光标C = NULL;
    尝试{
        C = connection_chronica.rawQuery（sSQL，NULL）;
    }赶上（SQLiteException E）{
        Log.v（SQLite的EXCETION，e.getMessage（））;
    }
    c.moveToFirst（）;
    Log.v（DEBUG负荷高速缓存，sIdentifier：+ sIdentifier）;
    字节[] BDATA = NULL;
    尝试{
        BDATA = c.getBlob（0）;
    }赶上（例外五）{
        e.printStackTrace（）;
    }
    对象o = NULL;    如果（BDATA！= NULL）{
        ByteArrayInputStream的BOS =新ByteArrayInputStream进行（BDATA）;
        ObjectInputStream的OIS;
        尝试{
            OIS =新的ObjectInputStream（BOS）;
            O = ois.readObject（）;        }赶上（StreamCorruptedException E）{
            // TODO自动生成catch块
            e.printStackTrace（）;
        }赶上（IOException异常五）{
            // TODO自动生成catch块
            e.printStackTrace（）;
        }赶上（ClassNotFoundException的E）{
            // TODO自动生成catch块
            e.printStackTrace（）;
        }
    }    c.close（）;
    返回O;}
 

我想优化读取速度，我发现文章mentoining simpleQueryForBlobFileDescriptor。

我的问题：这是否帮助我阅读BLOBS更快？如果是的话我如何使用它？

从其他职位举例：

  SQLiteStatement GET = mDb.compileStatement（
    选择blobColumn+
    FROM tableName值+
    WHE​​RE _id = 1+
    LIMIT 1
）;ParcelFileDescriptor结果= get.simpleQueryForBlobFileDescriptor（）;
FIS的FileInputStream =新的FileInputStream（result.getFileDescriptor（））; //读到像任何其他
 

解决方案

我的测试结果说，它的速度较慢。

长期测试后，我发现，在使用simpleQueryForBlobFileDescriptor较慢。见下code。我的老code例如读取390毫秒一个blob和新的code。与simpleQueryForBlobFileDescriptor读取805毫秒同一斑点。我读的地方，
simpleQueryForBlobFileDescriptor应该是一滴读数非常快，但这似乎不是在我的测试。 Perhabs我不这样做是否正确？ （ 我希望如此 ）。任何其他提示。

 公共对象getCachefromDb_old（字符串sIdentifier）{    Log.v（DEBUG LOAD BLOB，开始：+ sIdentifier）;
    对象o = NULL;
    尝试{
        // Erstelle EIN SQLStatemant麻省理工学院einer InClause
        字符串sSQL ='+ sIdentifier +选择从cache表，其中标识=缓存';
        SQLiteStatement GET = connection_chronica.compileStatement（sSQL）;
        ParcelFileDescriptor结果= get.simpleQueryForBlobFileDescriptor（）;
        FIS的FileInputStream =新的FileInputStream（result.getFileDescriptor（））;
        ObjectInputStream的inStream中=新的ObjectInputStream（FIS）;
        O = inStream.readObject（）;    }赶上（StreamCorruptedException E1）{
        // TODO自动生成catch块
        e1.printStackTrace（）;
    }赶上（IOException异常E1）{
        // TODO自动生成catch块
        e1.printStackTrace（）;
    }赶上（ClassNotFoundException的E）{
        // TODO自动生成catch块
        e.printStackTrace（）;
    }
    Log.v（DEBUG LOAD BLOB，结束：+ sIdentifier）;    返回O;}
 

I am reading blobs with size between 100kb and 1000kb from SQlite in my Android App using the following code :

public Object getCachefromDb(String sIdentifier){

    String sSQL = " Select cache from cachtable where identifier='" + sIdentifier + "'";

    Cursor c = null;
    try {
        c = connection_chronica.rawQuery(sSQL, null);
    } catch (SQLiteException e) {
        Log.v("SQLite Excetion", e.getMessage());
    }


    c.moveToFirst();
    Log.v("DEBUG load Cache","sIdentifier : " + sIdentifier);
    byte[] bData=null;
    try{
        bData = c.getBlob(0);
    }catch(Exception e){
        e.printStackTrace();
    }
    Object o = null;

    if (bData!=null){
        ByteArrayInputStream bos = new ByteArrayInputStream(bData);
        ObjectInputStream ois;
        try {
            ois = new ObjectInputStream(bos);
            o=ois.readObject();

        } catch (StreamCorruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    c.close();
    return o;

}

I would like to optimize the speed of reading and I found articles mentoining simpleQueryForBlobFileDescriptor.

My question : Does this help me reading BLOBS faster ? and if so how can I use it ?

Example from other posts:

SQLiteStatement get = mDb.compileStatement(
    "SELECT blobColumn" + 
    " FROM tableName" +
    " WHERE _id = 1" +
    " LIMIT 1"
);

ParcelFileDescriptor result = get.simpleQueryForBlobFileDescriptor();
FileInputStream fis = new FileInputStream(result.getFileDescriptor()); // read like any other

解决方案

My Tests results says its slower.

After long testing I found out, that using simpleQueryForBlobFileDescriptor is slower. See following code. My old code for example reads a blob in 390 miliseconds and the new code with simpleQueryForBlobFileDescriptor reads the same blob in 805 ms. I read somewhere that simpleQueryForBlobFileDescriptor should be very fast for blob readings, but this seems not to be in my tests. Perhabs I am not doing it properly ? ( I hope so ). Any other hints.

public Object getCachefromDb_old(String sIdentifier){

    Log.v("DEBUG LOAD BLOB","Start : " + sIdentifier);
    Object o = null;
    try {
        // Erstelle ein SQLStatemant mit einer InClause
        String sSQL = " Select cache from cachetable where identifier='" + sIdentifier + "'";
        SQLiteStatement get = connection_chronica.compileStatement(sSQL);
        ParcelFileDescriptor result = get.simpleQueryForBlobFileDescriptor();
        FileInputStream fis = new FileInputStream(result.getFileDescriptor());
        ObjectInputStream inStream = new ObjectInputStream(fis);
        o=inStream.readObject();

    } catch (StreamCorruptedException e1) {
        // TODO Auto-generated catch block
        e1.printStackTrace();
    } catch (IOException e1) {
        // TODO Auto-generated catch block
        e1.printStackTrace();
    } catch (ClassNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    Log.v("DEBUG LOAD BLOB","End : " + sIdentifier);

    return o;

}

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