ODAC seems to be caching table schema?

问题

I'm using Oracle's ODAC.NET for a .NET 3.5 project against an Oracle 11 Express database, and I'm seeing behavior that I can't explain (and can't seem to work around).

ODAC should be the latest, I just pulled it 3 days ago, but the versions are as follows:

Oracle.DataAccess.dll version 2.112.3.0 (release 5)
oci.dll (instant client) version 11.2.0.1

I have a Table, People, that has 3 columns:

ID
FirstName
LastName

In code I run an ALTER TABLE command, using OracleCommand.ExecuteNonQuery, to add a new column named "MIDDLE_NAME" to the table. That command succeeds. If I look at the table with Oracle SQL Developer, the columns shows up. All well and good.

Now if I run use OracleCommand.ExecuteReader with a command text of SELECT * FROM People right after I do the alter table, I get back data with only 3 columns, not 4!

Here is code that reproduces the problem:

public void FieldTest()
{
    var sql1 = "CREATE TABLE People (" +
        "ID NUMBER PRIMARY KEY, " +
        "FirstName NVARCHAR2 (200), " +
        "LastName NVARCHAR2 (200) NOT NULL)";

    var sql2 = "ALTER TABLE People " +
        "ADD Middle_Name NUMBER";

    var sql3 = "SELECT * FROM People";

    var sql4 = "SELECT column_name FROM all_tab_cols WHERE table_name = 'PEOPLE'";

    var cnInfo = new OracleConnectionInfo("192.168.10.246", 1521, "XE", "system", "password");
    var connectionString = BuildConnectionString(cnInfo);

    using (var connection = new OracleConnection(connectionString))
    {
        connection.Open();

        using (var create = new OracleCommand(sql1, connection))
        {
            create.ExecuteNonQuery();
        }

        using (var get = new OracleCommand(sql3, connection))
        {
            using (var reader = get.ExecuteReader())
            {
                Debug.WriteLine("Columns: " + reader.FieldCount);
                // outputs 3, which is right
            }
        }

        using (var alter = new OracleCommand(sql2, connection))
        {
            alter.ExecuteNonQuery();
        }

        using (var get = new OracleCommand(sql3, connection))
        {
            using (var reader = get.ExecuteReader())
            {
                Debug.WriteLine("Columns: " + reader.FieldCount);
                // outputs 3, which is *wrong* <---- Here's the problem
            }
        }

        using (var cols = new OracleCommand(sql4, connection))
        {
            using (var reader = cols.ExecuteReader())
            {
                int count = 0;

                while (reader.Read())
                {
                    count++;
                    Debug.WriteLine("Col: " + reader.GetString(0));
                }
                Debug.WriteLine("Columns: " + count.ToString());
                // outputs 4, which is right
            }
        }
    }
}

I've tried some things to prevent the behavior, and none of them give me back the 4th column:

I close the connection and re-open it
I use a new OracleConnection for the SELECT than for the ALTER
I use the same OracleConnection for the SELECT and for the ALTER
I use a new OracleCommand for the SELECT than for the ALTER
I use the same OracleCommand for the SELECT and for the ALTER
I call PurgeStatementCache on the connection between the ALTER and SELECT
I call FlushCache on the connection between the ALTER and SELECT
I explicitly Close and Dispose the OracleCommand and OracleConnection (as opposed to the using block) used for the ALTER and SELECT
Restarted the calling PC and the PC hosting the Oracle database.

If I look at the column list by doing a SELECT * FROM all_tab_cols, the new column is there.

The only thing that seems to work reliably is closing the app and re-starting it (well it's from a unit test, but it's a shutdown and restart of the test host). Then I get that 4th column. Sometimes I can use breakpoints and re-execute queries and the 4th column will appear, but nothing that is specifically repeatable with straight execution of code (meaning without setting a break point and moving the execution point back up).

Something in the bowels of ODAC seems to be caching the schema of that table, but I can figure out what, why or how to prevent it. Anyone have any experience with this, or ideas how I might prevent it?

回答1:

Maybe post some of your C# code. The following is a test that behaves as expected, meaning I can see the new column immediately after adding it. This is using odp 11.2 rel 5 hitting an 11g db, using 4.0 framework:

The test table is:

CREATE TABLE T1
(
  DTE  DATE default sysdate
);

Drop and recreate it after each run of the following C# code (a bit dirty but anyway):

string connStr = "User Id=xxx;Password=yyy;Data Source=my11gDb;";
using (OracleConnection con = new OracleConnection(connStr))
{
    string s = "ALTER TABLE T1 ADD (added_col VARCHAR2(10))";
    using (OracleCommand cmd = new OracleCommand(s, con))
    {
        con.Open();
        cmd.ExecuteNonQuery();

        string s2 = "select column_name from all_tab_columns where table_name = 'T1'";
        //con.FlushCache(); // doesn't seem to matter, works with or without

        using (OracleCommand cmd2 = new OracleCommand(s2, con))
        {
            OracleDataReader rdr = cmd2.ExecuteReader();

            for (int i = 0; rdr.Read(); i++)
            {
                Console.WriteLine("Column {0} => {1}",i+1,rdr.GetString(0));
            }
            rdr.Close();
        }
    }
}

Output:

Column 1 => DTE
Column 2 => ADDED_COL

Edit: Ah, ok, I see what you're saying, it looks like statement caching. I played around with changing the cache size to 0 (in conn string, use "Statement Cache Size=0"), and also tried cmd.AddToStatementCache = false, but these did not work.

One thing that does work is to use a slightly different string, like adding a space. I know its a hack, but this is all I can get to work for me anyway.

Try your example with:

var sql3 = "SELECT * FROM People";
var sql5 = "SELECT * FROM People "; // note extra space

And use sql3 before adding column, and sql5 after adding a column.

Hope that helps

回答2:

I know this answer comes years later but if new readers run into problems with caching try setting:

Metadata Pooling = false, Self Tuning = False and Statement Cache Size = 0

...in the connection string. Keep in mind that there are performance implications for doing so.

https://docs.oracle.com/database/122/ODPNT/featConnecting.htm#GUID-0CFEB161-68EF-4BC2-8943-3BDFFB878602

来源：https://stackoverflow.com/questions/16859567/odac-seems-to-be-caching-table-schema

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