H2Fulltext.java

/*
 * (C) Copyright 2006-2016 Nuxeo SA (http://nuxeo.com/) and others.
 *
 * 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.
 *
 * Contributors:
 *     H2 Group
 *     Florent Guillaume
 */
package org.nuxeo.ecm.core.storage.sql.db;

import java.io.IOException;
import java.io.Reader;
import java.lang.reflect.Constructor;
import java.nio.file.Paths;
import java.sql.Clob;
import java.sql.Connection;
import java.sql.DatabaseMetaData;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.sql.Types;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.lucene.analysis.Analyzer;
import org.apache.lucene.document.Document;
import org.apache.lucene.document.Field;
import org.apache.lucene.document.StringField;
import org.apache.lucene.document.TextField;
import org.apache.lucene.index.DirectoryReader;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.IndexWriter;
import org.apache.lucene.index.IndexWriterConfig;
import org.apache.lucene.index.IndexWriterConfig.OpenMode;
import org.apache.lucene.index.LeafReaderContext;
import org.apache.lucene.index.Term;
import org.apache.lucene.queryparser.classic.ParseException;
import org.apache.lucene.queryparser.classic.QueryParser;
import org.apache.lucene.search.BooleanClause;
import org.apache.lucene.search.BooleanQuery;
import org.apache.lucene.search.Collector;
import org.apache.lucene.search.IndexSearcher;
import org.apache.lucene.search.LeafCollector;
import org.apache.lucene.search.Scorer;
import org.apache.lucene.store.Directory;
import org.apache.lucene.store.FSDirectory;
import org.apache.lucene.store.LockObtainFailedException;
import org.apache.lucene.store.RAMDirectory;
import org.h2.message.DbException;
import org.h2.store.fs.FileUtils;
import org.h2.tools.SimpleResultSet;
import org.h2.util.IOUtils;
import org.h2.util.StringUtils;

/**
 * An optimized Lucene-based fulltext indexing trigger and search.
 */
public class H2Fulltext {

    private static final Map<String, Analyzer> analyzers = new ConcurrentHashMap<>();

    private static final Map<String, IndexWriter> indexWriters = new ConcurrentHashMap<>();

    private static final String FT_SCHEMA = "NXFT";

    private static final String FT_TABLE = FT_SCHEMA + ".INDEXES";

    private static final String PREFIX = "NXFT_";

    private static final String FIELD_KEY = "KEY";

    private static final String FIELD_TEXT = "TEXT";

    private static final String DEFAULT_INDEX_NAME = "PUBLIC_FULLTEXT_default";

    private static final String COL_KEY = "KEY";

    // Utility class.
    private H2Fulltext() {
    }

    /**
     * Initializes fulltext search functionality for this database. This adds the following Java functions to the
     * database:
     * <ul>
     * <li>NXFT_CREATE_INDEX(nameString, schemaString, tableString, columnListString, analyzerString)</li>
     * <li>NXFT_REINDEX()</li>
     * <li>NXFT_DROP_ALL()</li>
     * <li>NXFT_SEARCH(queryString, limitInt, offsetInt): result set</li>
     * </ul>
     * It also adds a schema NXFT to the database where bookkeeping information is stored. This function may be called
     * from a Java application, or by using the SQL statements:
     *
     * <pre>
     *  CREATE ALIAS IF NOT EXISTS NXFT_INIT FOR
     *      "org.nuxeo.ecm.core.storage.sql.db.H2Fulltext.init";
     *  CALL NXFT_INIT();
     * </pre>
     */
    public static void init(Connection conn) throws SQLException {
        try (Statement st = conn.createStatement()) {
            st.execute("CREATE SCHEMA IF NOT EXISTS " + FT_SCHEMA);
            st.execute("CREATE TABLE IF NOT EXISTS " + FT_TABLE
                    + "(NAME VARCHAR, SCHEMA VARCHAR, TABLE VARCHAR, COLUMNS VARCHAR, "
                    + "ANALYZER VARCHAR, PRIMARY KEY(NAME))");
            // BBB migrate old table without the "NAME" column
            try (ResultSet rs = st.executeQuery("SELECT * FROM INFORMATION_SCHEMA.COLUMNS WHERE " + "TABLE_SCHEMA = '"
                    + FT_SCHEMA + "' AND TABLE_NAME = 'INDEXES' AND COLUMN_NAME = 'NAME'")) {
                if (!rs.next()) {
                    // BBB no NAME column, alter table to create it
                    st.execute("ALTER TABLE " + FT_TABLE + " ADD COLUMN NAME VARCHAR");
                    st.execute("UPDATE " + FT_TABLE + " SET NAME = '" + DEFAULT_INDEX_NAME + "'");
                }
            }

            String className = H2Fulltext.class.getName();
            st.execute("CREATE ALIAS IF NOT EXISTS " + PREFIX + "CREATE_INDEX FOR \"" + className + ".createIndex\"");
            st.execute("CREATE ALIAS IF NOT EXISTS " + PREFIX + "REINDEX FOR \"" + className + ".reindex\"");
            st.execute("CREATE ALIAS IF NOT EXISTS " + PREFIX + "DROP_ALL FOR \"" + className + ".dropAll\"");
            st.execute("CREATE ALIAS IF NOT EXISTS " + PREFIX + "SEARCH FOR \"" + className + ".search\"");
        }
    }

    // ----- static methods called directly to initialize fulltext -----

    /**
     * Creates a fulltext index for a table and column list.
     * <p>
     * A table may have any number of indexes at a time, but the index name must be unique. If the index already exists,
     * nothing is done, otherwise the index is created and populated from existing data.
     * <p>
     * Usually called through:
     *
     * <pre>
     *   CALL NXFT_CREATE_INDEX('indexname', 'myschema', 'mytable', ('col1', 'col2'), 'lucene.analyzer');
     * </pre>
     *
     * @param conn the connection
     * @param indexName the index name
     * @param schema the schema name of the table
     * @param table the table name
     * @param columns the column list
     * @param analyzer the Lucene fulltext analyzer class
     */
    public static void createIndex(Connection conn, String indexName, String schema, String table, String columns,
            String analyzer) throws SQLException {
        if (indexName == null) {
            indexName = DEFAULT_INDEX_NAME;
        }
        columns = columns.replace("(", "").replace(")", "").replace(" ", "");
        try (PreparedStatement ps = conn.prepareStatement("DELETE FROM " + FT_TABLE + " WHERE NAME = ?")) {
            ps.setString(1, indexName);
            ps.execute();
        }
        try (PreparedStatement ps = conn.prepareStatement(
                "INSERT INTO " + FT_TABLE + "(NAME, SCHEMA, TABLE, COLUMNS, ANALYZER) VALUES(?, ?, ?, ?, ?)")) {
            ps.setString(1, indexName);
            ps.setString(2, schema);
            ps.setString(3, table);
            ps.setString(4, columns);
            ps.setString(5, analyzer);
            ps.execute();
        }
        createTrigger(conn, schema, table);
    }

    /**
     * Re-creates the fulltext index for this database.
     */
    public static void reindex(Connection conn) throws SQLException {
        removeAllTriggers(conn);
        removeIndexFiles(conn);
        try (Statement st = conn.createStatement()) {
            try (ResultSet rs = st.executeQuery("SELECT * FROM " + FT_TABLE)) {
                Set<String> done = new HashSet<>();
                while (rs.next()) {
                    String schema = rs.getString("SCHEMA");
                    String table = rs.getString("TABLE");
                    String key = schema + '.' + table;
                    if (!done.add(key)) {
                        continue;
                    }
                    createTrigger(conn, schema, table);
                    indexExistingRows(conn, schema, table);
                }
            }
        }
    }

    private static void indexExistingRows(Connection conn, String schema, String table) throws SQLException {
        Trigger trigger = new Trigger();
        trigger.init(conn, schema, null, table, false, org.h2.api.Trigger.INSERT);
        try (Statement st = conn.createStatement()) {
            try (ResultSet rs = st.executeQuery("SELECT * FROM " + StringUtils.quoteIdentifier(schema) + '.'
                    + StringUtils.quoteIdentifier(table))) {
                int n = rs.getMetaData().getColumnCount();
                while (rs.next()) {
                    Object[] row = new Object[n];
                    for (int i = 0; i < n; i++) {
                        row[i] = rs.getObject(i + 1);
                    }
                    trigger.fire(conn, null, row);
                }
            }
        }
    }

    /**
     * Creates a trigger for the indexes on a table.
     * <p>
     * Usually called through:
     *
     * <pre>
     *   CALL NXFT_CREATE_TRIGGERS('myschema', 'mytable');
     * </pre>
     *
     * @param conn the connection
     * @param schema the schema name of the table
     * @param table the table name
     */
    private static void createTrigger(Connection conn, String schema, String table) throws SQLException {
        try (Statement st = conn.createStatement()) {
            schema = StringUtils.quoteIdentifier(schema);
            String trigger = schema + '.' + StringUtils.quoteIdentifier(PREFIX + table);
            st.execute("DROP TRIGGER IF EXISTS " + trigger);
            st.execute(String.format(
                    "CREATE TRIGGER %s " + "AFTER INSERT, UPDATE, DELETE ON %s.%s " + "FOR EACH ROW CALL \"%s\"",
                    trigger, schema, StringUtils.quoteIdentifier(table), H2Fulltext.Trigger.class.getName()));
        }
    }

    private static void removeAllTriggers(Connection conn) throws SQLException {
        try (Statement st = conn.createStatement()) {
            try (ResultSet rs = st.executeQuery("SELECT * FROM INFORMATION_SCHEMA.TRIGGERS")) {
                try (Statement st2 = conn.createStatement()) {
                    while (rs.next()) {
                        String trigger = rs.getString("TRIGGER_NAME");
                        if (trigger.startsWith(PREFIX)) {
                            st2.execute("DROP TRIGGER " + StringUtils.quoteIdentifier(rs.getString("TRIGGER_SCHEMA"))
                                    + "." + trigger);
                        }
                    }
                }
            }
        }
    }

    /**
     * Drops all fulltext indexes from the database.
     */
    public static void dropAll(Connection conn) throws SQLException {
        try (Statement st = conn.createStatement()) {
            st.execute("DROP SCHEMA IF EXISTS " + FT_SCHEMA);
        }
        removeAllTriggers(conn);
        removeIndexFiles(conn);
    }

    private static String fieldForIndex(String indexName) {
        if (DEFAULT_INDEX_NAME.equals(indexName)) {
            return FIELD_TEXT;
        } else {
            return FIELD_TEXT + '_' + indexName;
        }
    }

    /**
     * Searches from the given full text index. The returned result set has a single ID column which holds the keys for
     * the matching rows.
     * <p>
     * Usually called through:
     *
     * <pre>
     *   SELECT * FROM NXFT_SEARCH(name, 'text');
     * </pre>
     *
     * @param conn the connection
     * @param indexName the index name
     * @param text the search query
     * @return the result set
     */
    public static ResultSet search(Connection conn, String indexName, String text) throws SQLException {
        DatabaseMetaData meta = conn.getMetaData();
        if (indexName == null) {
            indexName = DEFAULT_INDEX_NAME;
        }

        String schema;
        String table;
        String analyzerName;

        // find schema, table and analyzer
        try (PreparedStatement ps = conn.prepareStatement(
                "SELECT SCHEMA, TABLE, ANALYZER FROM " + FT_TABLE + " WHERE NAME = ?")) {
            ps.setString(1, indexName);
            try (ResultSet res = ps.executeQuery()) {
                if (!res.next()) {
                    throw new SQLException("No such index: " + indexName);
                }
                schema = res.getString(1);
                table = res.getString(2);
                analyzerName = res.getString(3);
            }
        }

        int type = getPrimaryKeyType(meta, schema, table);
        SimpleResultSet rs = new SimpleResultSet();
        rs.addColumn(COL_KEY, type, 0, 0);

        if (meta.getURL().startsWith("jdbc:columnlist:")) {
            // this is just to query the result set columns
            return rs;
        }

        // flush changes
        final IndexWriter writer = getIndexWriter(getIndexName(conn), getIndexPath(conn), analyzerName);
        if (writer.hasUncommittedChanges()) {
            try {
                writer.commit();
            } catch (IOException cause) {
                throw convertException(cause);
            }
        }

        // search index
        try {
            BooleanQuery.Builder queryBuilder = new BooleanQuery.Builder();
            String defaultField = fieldForIndex(indexName);
            Analyzer analyzer = getAnalyzer(analyzerName);
            QueryParser parser = new QueryParser(defaultField, analyzer);
            queryBuilder.add(parser.parse(text), BooleanClause.Occur.MUST);

            try (IndexReader reader = DirectoryReader.open(writer.getDirectory())) {
                IndexSearcher searcher = new IndexSearcher(reader);
                Collector collector = new ResultSetCollector(rs, reader, type);
                searcher.search(queryBuilder.build(), collector);
            }
        } catch (SQLException | ParseException | IOException e) {
            throw convertException(e);
        }
        return rs;
    }

    protected static class ResultSetCollector implements Collector, LeafCollector {
        protected final SimpleResultSet rs;

        protected IndexReader reader;

        protected int type;

        protected int docBase;

        public ResultSetCollector(SimpleResultSet rs, IndexReader reader, int type) {
            this.rs = rs;
            this.reader = reader;
            this.type = type;
        }

        @Override
        public LeafCollector getLeafCollector(LeafReaderContext context) throws IOException {
            docBase = context.docBase;
            return this;
        }

        @Override
        public void setScorer(Scorer scorer) {
        }

        @Override
        public boolean needsScores() {
            return false;
        }

        @Override
        public void collect(int docID) throws IOException {
            docID += docBase;
            Document doc = reader.document(docID, Collections.singleton(FIELD_KEY));
            Object key;
            try {
                key = asObject(doc.get(FIELD_KEY), type);
                rs.addRow(key);
            } catch (SQLException e) {
                throw new IOException(e);
            }
        }
    }

    private static int getPrimaryKeyType(DatabaseMetaData meta, String schema, String table) throws SQLException {
        // find primary key name
        String primaryKeyName = null;
        try (ResultSet rs = meta.getPrimaryKeys(null, schema, table)) {
            while (rs.next()) {
                if (primaryKeyName != null) {
                    throw new SQLException("Can only index primary keys on one column for " + schema + '.' + table);
                }
                primaryKeyName = rs.getString("COLUMN_NAME");
            }
            if (primaryKeyName == null) {
                throw new SQLException("No primary key for " + schema + '.' + table);
            }
        }
        // find primary key type
        try (ResultSet rs = meta.getColumns(null, schema, table, primaryKeyName)) {
            if (!rs.next()) {
                throw new SQLException("Could not find primary key");
            }
            return rs.getInt("DATA_TYPE");
        }
    }

    private static Analyzer getAnalyzer(String analyzerName) throws SQLException {
        Analyzer analyzer = analyzers.get(analyzerName);
        if (analyzer == null) {
            try {
                Class<?> klass = Class.forName(analyzerName);
                Constructor<?> constructor = klass.getConstructor();
                analyzer = (Analyzer) constructor.newInstance();
            } catch (ReflectiveOperationException e) {
                throw new SQLException(e.toString());
            }
            analyzers.put(analyzerName, analyzer);
        }
        return analyzer;
    }

    protected static String getIndexName(Connection conn) throws SQLException {
        String catalog = conn.getCatalog();
        if (catalog == null) {
            catalog = "default";
        }
        return catalog;
    }

    protected static String getIndexPath(Connection conn) throws SQLException {
        try (Statement st = conn.createStatement()) {
            try (ResultSet rs = st.executeQuery("CALL DATABASE_PATH()")) {
                rs.next();
                String path = rs.getString(1);
                if (path == null) {
                    return null;
                }
                return path + ".lucene";
            }
        }

    }

    private static IndexWriter getIndexWriter(String name, String path, String analyzer) throws SQLException {
        IndexWriter indexWriter = indexWriters.get(name);
        if (indexWriter != null) {
            return indexWriter;
        }
        synchronized (indexWriters) {
            indexWriter = indexWriters.get(name);
            if (indexWriter != null) {
                return indexWriter;
            }
            try {
                Directory dir = path == null ? new RAMDirectory() : FSDirectory.open(Paths.get(path));
                Analyzer an = getAnalyzer(analyzer);
                IndexWriterConfig iwc = new IndexWriterConfig(an);
                iwc.setOpenMode(OpenMode.CREATE_OR_APPEND);
                indexWriter = new IndexWriter(dir, iwc);
            } catch (LockObtainFailedException e) {
                throw convertException("Cannot open fulltext index " + path, e);
            } catch (IOException e) {
                throw convertException(e);
            }
            indexWriters.put(name, indexWriter);
            return indexWriter;
        }
    }

    private static void removeIndexFiles(Connection conn) throws SQLException {
        String path = getIndexPath(conn);
        try {
            IndexWriter index = indexWriters.remove(path);
            if (index != null) {
                try {
                    index.close();
                } catch (IOException e) {
                    throw convertException(e);
                }
            }
        } finally {
            FileUtils.deleteRecursive(path, false);
        }
    }

    private static SQLException convertException(Exception e) {
        return convertException("Error while indexing document", e);
    }

    private static SQLException convertException(String message, Exception e) {
        SQLException e2 = new SQLException(message);
        e2.initCause(e);
        return e2;
    }

    protected static String asString(Object data, int type) throws SQLException {
        if (data == null) {
            return "";
        }
        switch (type) {
        case Types.BIT:
        case Types.BOOLEAN:
        case Types.INTEGER:
        case Types.BIGINT:
        case Types.DECIMAL:
        case Types.DOUBLE:
        case Types.FLOAT:
        case Types.NUMERIC:
        case Types.REAL:
        case Types.SMALLINT:
        case Types.TINYINT:
        case Types.DATE:
        case Types.TIME:
        case Types.TIMESTAMP:
        case Types.LONGVARCHAR:
        case Types.CHAR:
        case Types.VARCHAR:
            return data.toString();
        case Types.CLOB:
            try {
                if (data instanceof Clob) {
                    data = ((Clob) data).getCharacterStream();
                }
                return IOUtils.readStringAndClose((Reader) data, -1);
            } catch (IOException e) {
                throw DbException.convert(e);
            }
        case Types.VARBINARY:
        case Types.LONGVARBINARY:
        case Types.BINARY:
        case Types.JAVA_OBJECT:
        case Types.OTHER:
        case Types.BLOB:
        case Types.STRUCT:
        case Types.REF:
        case Types.NULL:
        case Types.ARRAY:
        case Types.DATALINK:
        case Types.DISTINCT:
            throw new SQLException("Unsupported column data type: " + type);
        default:
            return "";
        }
    }

    // simple cases only, used for primary key
    private static Object asObject(String string, int type) throws SQLException {
        switch (type) {
        case Types.BIGINT:
            return Long.valueOf(string);
        case Types.INTEGER:
        case Types.SMALLINT:
        case Types.TINYINT:
            return Integer.valueOf(string);
        case Types.LONGVARCHAR:
        case Types.CHAR:
        case Types.VARCHAR:
            return string;
        default:
            throw new SQLException("Unsupport data type for primary key: " + type);
        }
    }

    /**
     * Trigger used to update the lucene index upon row change.
     */
    public static class Trigger implements org.h2.api.Trigger {

        private static final Log log = LogFactory.getLog(Trigger.class);

        private String indexName;

        private String indexPath;

        private IndexWriter indexWriter;

        // DEBUG
        private Exception lastIndexWriterClose;

        // DEBUG
        private String lastIndexWriterCloseThread;

        /** Starting at 0. */
        private int primaryKeyIndex;

        private int primaryKeyType;

        private Map<String, int[]> columnTypes;

        private Map<String, int[]> columnIndices;

        /**
         * Trigger interface: initialization.
         */
        @Override
        public void init(Connection conn, String schema, String triggerName, String table, boolean before, int opType)
                throws SQLException {
            DatabaseMetaData meta = conn.getMetaData();

            // find primary key name
            String primaryKeyName = null;
            try (ResultSet rs = meta.getPrimaryKeys(null, schema, table)) {
                while (rs.next()) {
                    if (primaryKeyName != null) {
                        throw new SQLException(
                                "Can only index primary keys on one column for: " + schema + '.' + table);
                    }
                    primaryKeyName = rs.getString("COLUMN_NAME");
                }
                if (primaryKeyName == null) {
                    throw new SQLException("No primary key for " + schema + '.' + table);
                }
            }

            // find primary key type
            try (ResultSet rs = meta.getColumns(null, schema, table, primaryKeyName)) {
                if (!rs.next()) {
                    throw new SQLException("No primary key for: " + schema + '.' + table);
                }
                primaryKeyType = rs.getInt("DATA_TYPE");
                primaryKeyIndex = rs.getInt("ORDINAL_POSITION") - 1;
            }

            // find all columns info
            Map<String, Integer> allColumnTypes = new HashMap<>();
            Map<String, Integer> allColumnIndices = new HashMap<>();
            try (ResultSet rs = meta.getColumns(null, schema, table, null)) {
                while (rs.next()) {
                    String name = rs.getString("COLUMN_NAME");
                    int type = rs.getInt("DATA_TYPE");
                    int index = rs.getInt("ORDINAL_POSITION") - 1;
                    allColumnTypes.put(name, Integer.valueOf(type));
                    allColumnIndices.put(name, Integer.valueOf(index));
                }
            }

            // find columns configured for indexing
            try (PreparedStatement ps = conn.prepareStatement(
                    "SELECT NAME, COLUMNS, ANALYZER FROM " + FT_TABLE + " WHERE SCHEMA = ? AND TABLE = ?")) {
                ps.setString(1, schema);
                ps.setString(2, table);
                try (ResultSet rs = ps.executeQuery()) {
                    columnTypes = new HashMap<>();
                    columnIndices = new HashMap<>();
                    while (rs.next()) {
                        String index = rs.getString(1);
                        String columns = rs.getString(2);
                        String analyzerName = rs.getString(3);
                        List<String> columnNames = Arrays.asList(columns.split(","));

                        // find the columns' indices and types
                        int[] types = new int[columnNames.size()];
                        int[] indices = new int[columnNames.size()];
                        int i = 0;
                        for (String columnName : columnNames) {
                            types[i] = allColumnTypes.get(columnName).intValue();
                            indices[i] = allColumnIndices.get(columnName).intValue();
                            i++;
                        }
                        columnTypes.put(index, types);
                        columnIndices.put(index, indices);
                        // only one call actually needed for this:
                        indexName = getIndexName(conn);
                        indexPath = getIndexPath(conn);
                        indexWriter = getIndexWriter(indexName, indexPath, analyzerName);
                    }

                }
            }
        }

        /**
         * Trigger interface.
         */
        @Override
        public void fire(Connection conn, Object[] oldRow, Object[] newRow) throws SQLException {
            if (indexWriter == null) {
                throw new SQLException("Fulltext index was not initialized");
            }
            if (oldRow != null) {
                delete(oldRow);
            }
            if (newRow != null) {
                insert(newRow);
            }
        }

        private void insert(Object[] row) throws SQLException {
            Document doc = new Document();
            String key = asString(row[primaryKeyIndex], primaryKeyType);
            // StringField is not tokenized
            StringField keyField = new StringField(FIELD_KEY, key, Field.Store.YES);
            doc.add(keyField);

            // add fulltext for all indexes
            for (String indexName : columnTypes.keySet()) {
                int[] types = columnTypes.get(indexName);
                int[] indices = columnIndices.get(indexName);
                StringBuilder buf = new StringBuilder();
                for (int i = 0; i < types.length; i++) {
                    String data = asString(row[indices[i]], types[i]);
                    if (i > 0) {
                        buf.append(' ');
                    }
                    buf.append(data);
                }
                // TextField is tokenized
                TextField textField = new TextField(fieldForIndex(indexName), buf.toString(), Field.Store.NO);
                doc.add(textField);
            }

            try {
                indexWriter.addDocument(doc);
            } catch (IOException e) {
                throw convertException(e);
            } catch (org.apache.lucene.store.AlreadyClosedException e) {
                // DEBUG
                log.error("org.apache.lucene.store.AlreadyClosedException in thread " + Thread.currentThread().getName()
                        + ", last close was in thread " + lastIndexWriterCloseThread, lastIndexWriterClose);
                throw e;
            }
        }

        private void delete(Object[] row) throws SQLException {
            String primaryKey = asString(row[primaryKeyIndex], primaryKeyType);
            try {
                indexWriter.deleteDocuments(new Term(FIELD_KEY, primaryKey));
            } catch (IOException e) {
                throw convertException(e);
            }
        }

        @Override
        public void close() throws SQLException {
            if (indexWriter != null) {
                try {
                    // DEBUG
                    lastIndexWriterClose = new RuntimeException("debug stack trace");
                    lastIndexWriterCloseThread = Thread.currentThread().getName();
                    indexWriter.close();
                    indexWriter = null;
                } catch (IOException e) {
                    throw convertException(e);
                } finally {
                    indexWriters.remove(indexName);
                }
            }
        }

        @Override
        public void remove() {
            // ignore
        }
    }

}