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From "Kathey Marsden (JIRA)" <j...@apache.org>
Subject [jira] Issue Comment Edited: (DERBY-3753) select from table with integer primary key and blob column does not do sort avoidance
Date Thu, 06 Nov 2008 17:32:31 GMT

    [ https://issues.apache.org/jira/browse/DERBY-3753?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12645518#action_12645518
] 

kmarsden edited comment on DERBY-3753 at 11/6/08 9:30 AM:
----------------------------------------------------------------

Attached is a stand alone repro for this issue, but you have to look at the derby.log to see
the plans.   The first query in the log is without the optimizer directive. The second is
with the optimizer directive to use the index.  Without the optimizer directive the query
does a table scan and the cost is estimated to be less than that of using the index.  I thought
perhaps there would be a difference if I added more rows but with 1000 rows I get the same
result.

On first run, run
java Derby3753 load

On subsequent runs, no need to specify the load option.

      was (Author: kmarsden):
    Attached is a stand alone repro for this issue, but you have to look at the derby.log
to see the plans.   The first query in the log is without the optimizer directive. The second
is with the optimizer directive to use the index.  Without the optimizer directive the query
does a table scan and the cost is estimated to be less than that of using the index.  I thought
perhaps there would be a difference if I added more rows but with 1000 rows I get the same
result.


  
> select from table with integer primary key and blob column does not do sort avoidance
> -------------------------------------------------------------------------------------
>
>                 Key: DERBY-3753
>                 URL: https://issues.apache.org/jira/browse/DERBY-3753
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 10.3.3.0, 10.4.1.3, 10.5.0.0
>            Reporter: Kathey Marsden
>         Attachments: derby.log, Derby3753.java
>
>
> In working on DERBY-3732 I noticed that select from a table with a primary key and a
blob column does not do sort avoidance.  If you  remove the optimizer directive, this fixture
in BlobMemTest will run out of memory sorting if memory.BlobMemTest is run with 16M heap.
>  private void testBlobLength(boolean lengthless) throws SQLException, IOException, IllegalArgumentException,
IllegalAccessException, InvocationTargetException {
>         getConnection().setAutoCommit(false);
>         Statement s = createStatement();
>         s.executeUpdate("CREATE TABLE BLOBTAB (K INT CONSTRAINT PK PRIMARY KEY, B BLOB("
+ LONG_BLOB_LENGTH + "))");
>         
>         PreparedStatement ps = prepareStatement("INSERT INTO BLOBTAB VALUES(?,?)");
>         // We allocate 16MB for the test so use something bigger than that.
>         ps.setInt(1,1);
>         LoopingAlphabetStream stream = new LoopingAlphabetStream(LONG_BLOB_LENGTH);
>         if (lengthless) {
>             Method m = null;
>             try {
>                 Class c = ps.getClass();
>                 m = c.getMethod("setBinaryStream",new Class[] {Integer.TYPE,
>                             InputStream.class});                
>             } catch (NoSuchMethodException e) {
>                 // ignore method not found as method may not be present for 
>                 // jdk's lower than 1.6.
>                 println("Skipping lengthless insert because method is not available");
>                 return;                
>             }
>             m.invoke(ps, new Object[] {new Integer(2),stream});
>         }
>         else
>             ps.setBinaryStream(2, stream,LONG_BLOB_LENGTH);
>         ps.executeUpdate();
>         // insert a zero length blob.
>         ps.setInt(1, 2);
>         ps.setBytes(2, new byte[] {});
>         ps.executeUpdate();
>         // insert a null blob.
>         ps.setInt(1, 3);
>         ps.setBytes(2,null);
>         ps.executeUpdate();
>         // insert a short blob
>         ps.setInt(1, 4);
>         ps.setBytes(2, SHORT_BLOB_BYTES);
>         ps.executeUpdate();
>         // Currently need to use optimizer override to force use of the index.
>         // Derby should use sort avoidance and do it automatically, but there
>         // appears to be a bug.
>         ResultSet rs = s.executeQuery("SELECT K, LENGTH(B), B FROM BLOBTAB" +
>                 "-- DERBY-PROPERTIES constraint=pk\n ORDER BY K"); 
>         rs.next();
>         assertEquals(LONG_BLOB_LENGTH_STRING,rs.getString(2));
>         // make sure we can still access the blob after getting length.
>         // It should be ok because we reset the stream
>         InputStream rsstream = rs.getBinaryStream(3);
>         int len= 0;
>         byte[] buf = new byte[32672];
>         for (;;)  {
>                 int size = rsstream.read(buf);
>                 if (size == -1)
>                         break;
>                 len += size;
>                 int expectedValue = ((len -1) % 26) + 'a';
>                 if (size != 0)
>                     assertEquals(expectedValue,buf[size -1]);      
>         }
>         assertEquals(LONG_BLOB_LENGTH,len);
>         // empty blob
>         rs.next();
>         assertEquals("0",rs.getString(2));
>         byte[] bytes = rs.getBytes(3);
>         assertEquals(0, bytes.length);
>         // null blob
>         rs.next();
>         assertEquals(null,rs.getString(2));
>         bytes = rs.getBytes(3);
>         assertEquals(null,bytes);
>         // short blob
>         rs.next();
>         assertEquals("3",rs.getString(2));
>         bytes = rs.getBytes(3);
>         assertTrue(Arrays.equals(SHORT_BLOB_BYTES, bytes));
>         rs.close();         
>         
>         // Select just length without selecting the blob.
>         rs = s.executeQuery("SELECT K, LENGTH(B)  FROM BLOBTAB " +
>                 "ORDER BY K");
>         JDBC.assertFullResultSet(rs, new String [][] {{"1",LONG_BLOB_LENGTH_STRING},{"2","0"},
>                 {"3",null},{"4","3"}});
>     }

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