操作blob字段是否会产生大量redo,答案是不会，下面来做一个实验,测试数据库版本是11.2.0.1.0:

--创建一张表做测试之用

create table test_blob
(
id number,
tupian blob
);

import java.io.FileInputStream;
import java.io.OutputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

import oracle.sql.BLOB;

public class BlobExample {
    static final String driver_class  = "oracle.jdbc.driver.OracleDriver";
    static final String connectionURL = "jdbc:oracle:thin:@10.10.15.25:1521:orcl";
    static final String userID        = "test";
    static final String userPassword  = "test";

    private void insertTestBlob() {
        Connection conn=null;
        Statement stm=null;
        ResultSet rs=null;
        BLOB blob = null;
        FileInputStream fin=null;
        OutputStream out=null;
        try{
            conn = DriverManager.getConnection(connectionURL, userID, userPassword);
            stm = conn.createStatement();
            conn.setAutoCommit(false);
            String sql = "insert into test_blob values(1,EMPTY_BLOB())";
            stm.executeUpdate(sql);
            rs = stm.executeQuery("SELECT tupian FROM test_blob WHERE id=1 FOR UPDATE ");
           fin = new FileInputStream("d://20130317.jpg");
           byte[] blobBuf = new byte[(int)fin.available()];
           fin.read(blobBuf);
           fin.close();

           if(rs.next()) {
            blob = (oracle.sql.BLOB)rs.getBlob(1);
            out = blob.getBinaryOutputStream();
            out.write(blobBuf);
            out.close();
            conn.commit();
           }
        }catch(Exception e){
            e.printStackTrace();
        }finally{
            try {
                rs.close();
                stm.close();
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
    public static void main(String args[]){
        BlobExample  blobClobExample = new BlobExample();
        blobClobExample.insertTestBlob();
    }
}

insert into test_blob select * from test_blob;

insert into test_blob select * from test_blob;

.......

commit;

--准备dump block

select rowid,
dbms_rowid.rowid_object(rowid) object_id,
dbms_rowid.rowid_relative_fno(rowid) file_id,
dbms_rowid.rowid_block_number(rowid) block_id,
dbms_rowid.rowid_row_number(rowid) num
from test_blob;

--update之前blob的状态

alter session set tracefile_identifier = 'Look_For_Me';
alter system switch logfile;
alter system switch logfile;
alter system dump datafile 5 block 3274932;

--update之后blob的状态，同时测试一下，此时update产生了多少redo
select name, value
from v$mystat, v$statname
where v$mystat.statistic# = v$statname.statistic#
and v$statname.name = 'redo size'
update test_blob set tupian = null;
commit;

select name, value
from v$mystat, v$statname
where v$mystat.statistic# = v$statname.statistic#
and v$statname.name = 'redo size'

alter system switch logfile;
alter system switch logfile;
alter session set tracefile_identifier = 'Look_For_Me1';
alter system dump datafile 5 block 3274932;

测试结果：我传的图片是5.1M，一共产生了350条数据，都把blob置为空以后，共产生了7.6M的redo，很显然是blob的内容是没有产生redo的。

分析原理，得借助分析dump block的内容,可以看到设置blob字段为null后产生的redo只是类似col 1: [84]这些信息。

blob设置为空以前: