FetchOnBufferReadJdbcIndexInput.java

/*
 * Copyright 2004-2009 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.lucene.store.jdbc.index;

import java.io.IOException;
import java.sql.Blob;
import java.sql.PreparedStatement;
import java.sql.ResultSet;

import org.apache.lucene.store.jdbc.JdbcDirectory;
import org.apache.lucene.store.jdbc.JdbcFileEntrySettings;
import org.apache.lucene.store.jdbc.JdbcStoreException;
import org.apache.lucene.store.jdbc.support.JdbcTemplate;

/**
 * An <code>IndexInput</code> implementation, that for every buffer refill will go and fetch
 * the data from the database.
 *
 * @author kimchy
 */
public class FetchOnBufferReadJdbcIndexInput extends JdbcBufferedIndexInput {

    private String name;

    // lazy intialize the length
    private long totalLength = -1;

    private long position = 1;

    private JdbcDirectory jdbcDirectory;

    public void configure(String name, JdbcDirectory jdbcDirectory, JdbcFileEntrySettings settings) throws IOException {
        super.configure(name, jdbcDirectory, settings);
        this.jdbcDirectory = jdbcDirectory;
        this.name = name;
    }


    // Overriding refill here since we can execute a single query to get both the length and the buffer data
    // resulted in not the nicest OO design, where the buffer information is protected in the JdbcBufferedIndexInput class
    // and code duplication between this method and JdbcBufferedIndexInput.
    // Performance is much better this way!
    protected void refill() throws IOException {
        jdbcDirectory.getJdbcTemplate().executeSelect(jdbcDirectory.getTable().sqlSelectSizeValueByName(),
                new JdbcTemplate.ExecuteSelectCallback() {
                    public void fillPrepareStatement(PreparedStatement ps) throws Exception {
                        ps.setFetchSize(1);
                        ps.setString(1, name);
                    }

                    public Object execute(ResultSet rs) throws Exception {
                        // START read blob and update length if required
                        if (!rs.next()) {
                            throw new JdbcStoreException("No entry for [" + name + "] table " + jdbcDirectory.getTable());
                        }
                        synchronized (this) {
                            if (totalLength == -1) {
                                totalLength = rs.getLong(3);
                            }
                        }
                        // END read blob and update length if required

                        long start = bufferStart + bufferPosition;
                        long end = start + bufferSize;
                        if (end > length())                  // don't read past EOF
                            end = length();
                        bufferLength = (int) (end - start);
                        if (bufferLength <= 0)
                            throw new IOException("read past EOF");

                        if (buffer == null) {
                            buffer = new byte[bufferSize];          // allocate buffer lazily
                            seekInternal(bufferStart);
                        }
                        // START replace read internal
                        Blob blob = rs.getBlob(2);
                        readInternal(blob, buffer, 0, bufferLength);

                        bufferStart = start;
                        bufferPosition = 0;
                        return null;
                    }
                });
    }

    protected synchronized void readInternal(final byte[] b, final int offset, final int length) throws IOException {
        jdbcDirectory.getJdbcTemplate().executeSelect(jdbcDirectory.getTable().sqlSelectSizeValueByName(),
                new JdbcTemplate.ExecuteSelectCallback() {
                    public void fillPrepareStatement(PreparedStatement ps) throws Exception {
                        ps.setFetchSize(1);
                        ps.setString(1, name);
                    }

                    public Object execute(ResultSet rs) throws Exception {
                        if (!rs.next()) {
                            throw new JdbcStoreException("No entry for [" + name + "] table " + jdbcDirectory.getTable());
                        }
                        Blob blob = rs.getBlob(2);
                        readInternal(blob, b, offset, length);
                        synchronized (this) {
                            if (FetchOnBufferReadJdbcIndexInput.this.totalLength == -1) {
                                FetchOnBufferReadJdbcIndexInput.this.totalLength = rs.getLong(3);
                            }
                        }
                        return null;
                    }
                });
    }

    /**
     * A helper methods that already reads an open blob
     */
    private synchronized void readInternal(Blob blob, final byte[] b, final int offset, final int length) throws Exception {
        long curPos = getFilePointer();
        if (curPos + 1 != position) {
            position = curPos + 1;
        }
        byte[] bytesRead = blob.getBytes(position, length);
        if (bytesRead.length != length) {
            throw new IOException("read past EOF");
        }
        System.arraycopy(bytesRead, 0, b, offset, length);
        position += bytesRead.length;
    }

    protected void seekInternal(long pos) throws IOException {
        this.position = pos + 1;
    }

    public void close() throws IOException {
    }

    public synchronized long length() {
        if (totalLength == -1) {
            try {
                this.totalLength = jdbcDirectory.fileLength(name);
            } catch (IOException e) {
                // do nothing here for now, much better for performance
            }
        }
        return totalLength;
    }
}