log.java

hsql是很有名的嵌入式数据库

     */
    boolean hasCache() {
        return cache != null;
    }

    /**
     * Responsible for creating the cache instance.
     */
    DataFileCache getCache() throws HsqlException {

/*
        if (database.isFilesInJar()) {
            return null;
        }
*/
        if (cache == null) {
            cache = new DataFileCache(database, cacheFileName,
                                      backupFileName);

            cache.open(filesReadOnly);
        }

        return cache;
    }

    int getLogSize() {
        return (int) (maxLogSize / (1024 * 11024));
    }

    void setLogSize(int megas) {

        properties.setProperty("hsqldb.log_size", megas);

        maxLogSize = megas * 1024 * 1024;
    }

    int getScriptType() {
        return scriptFormat;
    }

    /**
     * Changing the script format results in a checkpoint, with the .script
     * file written in the new format.
     */
    void setScriptType(int type) throws HsqlException {

        if (database.isStoredFileAccess()) {
            return;
        }

        boolean needsCheckpoint = scriptFormat != type;

        scriptFormat = type;

        properties.setProperty("hsqldb.script_format", scriptFormat);

        if (needsCheckpoint) {
            checkpoint(false);
        }
    }

    /**
     * Write delay specifies the frequency of FileDescriptor.sync() calls.
     */
    int getWriteDelay() {
        return writeDelay;
    }

    void setWriteDelay(int delay) {

        writeDelay = delay;

        if (dbLogWriter != null) {
            synchLog();
            dbLogWriter.setWriteDelay(delay);
        }
    }

    /**
     * Various writeXXX() methods are used for logging statements.
     */
    void writeStatement(Session session, String s) throws HsqlException {

        if (s == null || s.length() == 0) {
            return;
        }

        try {
            dbLogWriter.writeLogStatement(session, s);
        } catch (IOException e) {
            throw Trace.error(Trace.FILE_IO_ERROR, logFileName);
        }

        if (maxLogSize > 0 && dbLogWriter.size() > maxLogSize) {
            checkpoint(false);
        }
    }

    void writeInsertStatement(Session session, Table t,
                              Object[] row) throws HsqlException {

        try {
            dbLogWriter.writeInsertStatement(session, t, row);
        } catch (IOException e) {
            throw Trace.error(Trace.FILE_IO_ERROR, logFileName);
        }

        if (maxLogSize > 0 && dbLogWriter.size() > maxLogSize) {
            checkpoint(false);
        }
    }

    void writeDeleteStatement(Session session, Table t,
                              Object[] row) throws HsqlException {

        try {
            dbLogWriter.writeDeleteStatement(session, t, row);
        } catch (IOException e) {
            throw Trace.error(Trace.FILE_IO_ERROR, logFileName);
        }

        if (maxLogSize > 0 && dbLogWriter.size() > maxLogSize) {
            checkpoint(false);
        }
    }

    void writeSequenceStatement(Session session,
                                NumberSequence s) throws HsqlException {

        try {
            dbLogWriter.writeSequenceStatement(session, s);
        } catch (IOException e) {
            throw Trace.error(Trace.FILE_IO_ERROR, logFileName);
        }

        if (maxLogSize > 0 && dbLogWriter.size() > maxLogSize) {
            checkpoint(false);
        }
    }

    void writeCommitStatement(Session session) throws HsqlException {

        try {
            dbLogWriter.writeCommitStatement(session);
        } catch (IOException e) {
            throw Trace.error(Trace.FILE_IO_ERROR, logFileName);
        }

        if (maxLogSize > 0 && dbLogWriter.size() > maxLogSize) {
            checkpoint(false);
        }
    }

    void synchLog() {

        if (dbLogWriter != null) {
            dbLogWriter.sync();
        }
    }

    /**
     * Wrappers for openning-starting / stoping-closing the log file and
     * writer.
     */
    private void openLog() throws HsqlException {

        if (filesReadOnly) {
            return;
        }

        try {
            dbLogWriter = ScriptWriterBase.newScriptWriter(database,
                    logFileName, false, false,
                    ScriptWriterBase.SCRIPT_TEXT_170);

            dbLogWriter.setWriteDelay(writeDelay);
            dbLogWriter.start();
        } catch (Exception e) {
            throw Trace.error(Trace.FILE_IO_ERROR, logFileName);
        }
    }

    private synchronized void closeLog() throws HsqlException {

        if (dbLogWriter != null) {
            dbLogWriter.close();
        }
    }

    /**
     * Write the .script file as .script.new.
     */
    private void writeScript(boolean full) throws HsqlException {

        String sNewName = scriptFileName + ".new";

        try {
            if (fa.isStreamElement(sNewName)) {
                fa.removeElement(sNewName);
            }
        } catch (IOException e) {
            database.logger.appLog.logContext(e);
        }

        //fredt - to do - flag for chache set index
        ScriptWriterBase scw = ScriptWriterBase.newScriptWriter(database,
            scriptFileName + ".new", full, true, scriptFormat);

        scw.writeAll();
        scw.close();
    }

    /**
     * Performs all the commands in the .script file.
     */
    private void processScript() throws HsqlException {

        ScriptReaderBase scr = null;

        try {
            if (database.isFilesInJar()
                    || fa.isStreamElement(scriptFileName)) {
                scr = ScriptReaderBase.newScriptReader(database,
                                                       scriptFileName,
                                                       scriptFormat);

                scr.readAll(database.sessionManager.getSysSession(null,
                        true));
                scr.close();
            }
        } catch (Throwable e) {
            if (scr != null) {
                scr.close();

                if (cache != null) {
                    cache.close(false);
                }

                closeAllTextCaches(false);
            }

            database.logger.appLog.logContext(e);

            if (e instanceof HsqlException) {
                throw (HsqlException) e;
            } else if (e instanceof IOException) {
                throw Trace.error(Trace.FILE_IO_ERROR, e.getMessage());
            } else if (e instanceof OutOfMemoryError) {
                throw Trace.error(Trace.OUT_OF_MEMORY);
            } else {
                throw Trace.error(Trace.GENERAL_ERROR, e.getMessage());
            }
        }
    }

    /**
     * Defrag large data files when the sum of .log and .data files is large.
     */
    private void processDataFile() throws HsqlException {

        if (cache == null || filesReadOnly || database.isStoredFileAccess()
                ||!fa.isStreamElement(logFileName)) {
            return;
        }

        File file       = new File(logFileName);
        long logLength  = file.length();
        long dataLength = cache.getFileFreePos();

        if (logLength + dataLength > cache.maxDataFileSize) {
            checkpoint(true);
        }
    }

    /**
     * Performs all the commands in the .log file.
     */
    private void processLog() throws HsqlException {

        if (!database.isFilesInJar() && fa.isStreamElement(logFileName)) {
            ScriptRunner.runScript(database, logFileName,
                                   ScriptWriterBase.SCRIPT_TEXT_170);
        }
    }

    /**
     * Restores a compressed backup or the .data file.
     */
    private void restoreBackup() throws HsqlException {

        // in case data file cannot be deleted, reset it
        DataFileCache.deleteOrResetFreePos(database, cacheFileName);

        try {
            ZipUnzipFile.decompressFile(backupFileName, cacheFileName,
                                        database.getFileAccess());
        } catch (Exception e) {
            throw Trace.error(Trace.FILE_IO_ERROR, Trace.Message_Pair,
                              new Object[] {
                backupFileName, e.getMessage()
            });
        }
    }

// fredt@users 20020221 - patch 513005 by sqlbob@users (RMP) - text tables
    private HashMap textCacheList = new HashMap();

    DataFileCache openTextCache(Table table, String source,
                                boolean readOnlyData,
                                boolean reversed) throws HsqlException {

        closeTextCache(table);

        if (!properties.isPropertyTrue("textdb.allow_full_path")) {
            if (source.indexOf("..") != -1) {
                throw (Trace.error(Trace.ACCESS_IS_DENIED, source));
            }

            String path = new File(
                new File(
                    database.getPath()
                    + ".properties").getAbsolutePath()).getParent();

            if (path != null) {
                source = path + File.separator + source;
            }
        }

        TextCache c;
        int       type;

        if (reversed) {
            c = new TextCache(table, source);
        } else {
            c = new TextCache(table, source);
        }

        c.open(readOnlyData || filesReadOnly);
        textCacheList.put(table.getName(), c);

        return c;
    }

    void closeTextCache(Table table) throws HsqlException {

        TextCache c = (TextCache) textCacheList.remove(table.getName());

        if (c != null) {
            c.close(true);
        }
    }

    private void closeAllTextCaches(boolean compact) throws HsqlException {

        Iterator it = textCacheList.values().iterator();

        while (it.hasNext()) {
            if (compact) {
                ((TextCache) it.next()).purge();
            } else {
                ((TextCache) it.next()).close(true);
            }
        }
    }

    private void reopenAllTextCaches() throws HsqlException {

        Iterator it = textCacheList.values().iterator();

        while (it.hasNext()) {
            ((TextCache) it.next()).reopen();
        }
    }

    private boolean isAnyTextCacheModified() {

        Iterator it = textCacheList.values().iterator();

        while (it.hasNext()) {
            if (((TextCache) it.next()).isFileModified()) {
                return true;
            }
        }

        return false;
    }
}