小编Sal*_*lah的帖子

我收到以下 MySQL 错误：

Too many keys specified; max 64 keys allowed.

是否可以增加 MySQL 中的最大索引大小，如果可以，那么我们该怎么做？

我需要在表中询问我的列jdbc类型,今天我循环抛出我的列,​​然后询问它的类型,请参阅下面的代码:

public int getColumnDataTypeFromDB(String columnName) {
    int datatype = 0;

    ResultSet columns = null;
    try {
        String schema =
            getMetaDataCatalogName() != null
                ? getMetaDataCatalogName()
                : getMetaDataSchemaName();

        if (TableManagerFactory.isCatalogBasedDatabase()) {
            columns =
                getMetaData().getColumns(
                    schema,
                    null,
                    tableName,
                    columnName);
        } else {
            columns =
                getMetaData().getColumns(
                    null,
                    schema,
                    tableName,
                    columnName);
        }
        //          columns =
        //              getMetaData().getColumns(getMetaDataCatalogName(), getMetaDataSchemaName(), tableName, columnName);
        if (columns.next()) {
            datatype = columns.getInt("DATA_TYPE");
        }
    } catch (SQLException ex) {
        Log.error(
            this,
            "Error while getting columns information: " + ex.getMessage(),
            ex);
        //return false; …

我有这个代码,这段代码基本上设置了限制,PreparedStatement以避免加载整个表数据.

PreparedStatement pstmt = null;
    ResultSet rs = null;
    try {
        pstmt = con.prepareStatement(sql, ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY);
        if (getDataSheet().isPagingEnabled()) {
            pstmt.setFetchSize(getDataSheet().getPageSize() + 1);
        }

        if (getDataSheet().isDisableTotalRowsCount() && maxRecords >= 0) {
            if (getDataSheet().isPagingEnabled()) {
                pstmt.setMaxRows(getCurrentPageSize());
            } else {
                pstmt.setMaxRows(maxRecords);
            }
        }

        //the rest of code.

    } catch(Exception ex) {
        //handle exception
    }

这段代码适用于所有数据库供应商,除了Oracle驱动程序中的一个案例,如果我使用setFetchSize了PreparedStatement,并且页面大小超过20000,则驱动程序抛出OutOfMemoryError

Caused by: java.lang.OutOfMemoryError: Java heap space
at oracle.jdbc.driver.PhysicalConnection.getCharBuffer(PhysicalConnection.java:7018)
at oracle.jdbc.driver.OracleStatement.prepareAccessors(OracleStatement.java:907)
at oracle.jdbc.driver.T4CTTIdcb.receiveCommon(T4CTTIdcb.java:261)
at oracle.jdbc.driver.T4CTTIdcb.receive(T4CTTIdcb.java:127)
at oracle.jdbc.driver.T4C8Oall.receive(T4C8Oall.java:992)
at oracle.jdbc.driver.T4CPreparedStatement.doOall8(T4CPreparedStatement.java:194)
at oracle.jdbc.driver.T4CPreparedStatement.executeForDescribe(T4CPreparedStatement.java:791)
at oracle.jdbc.driver.T4CPreparedStatement.executeMaybeDescribe(T4CPreparedStatement.java:866) …

我必须在我的项目中使用lucene创建全文搜索,所以我必须索引mysql数据库中的blob列(包含文件pdf,doc,xsl,xml和image),使用doc,xsl和xml我没有任何问题但是使用pdf文件我无法获得结果

    public class Indexfile {
  public static void main(String[] args) throws Exception {

        RemoteControlServiceConnection a = new RemoteControlServiceConnection(
                "jdbc:mysql://localhost:3306/Test","root", "root" );
        Connection conn = a.getConnexionMySQL();
        final File INDEX_DIR = new File("index");
        IndexWriter writer = new IndexWriter(INDEX_DIR,
                new StandardAnalyzer(),
                true);

        String query = "SELECT id, name ,document FROM Table_document";
        Statement statement = conn.createStatement();
        ResultSet result = statement.executeQuery(query);

        while (result.next()) {
            Document document = new Document();
            document.add(new Field("id", result.getString("id"), Field.Store.YES, Field.Index.NO));
            document.add(new Field("name", result.getString("name"), Field.Store.YES, Field.Index.TOKENIZED));
            document.add(new Field("document", result.getString("document"), Field.Store.YES, Field.Index.TOKENIZED));
             writer.addDocument(text); …