org.apache.derby.impl.store.raw.log

Class Scan

java.lang.Object

org.apache.derby.impl.store.raw.log.Scan

All Implemented Interfaces:

LogScan, StreamLogScan

public class Scan
extends java.lang.Object
implements StreamLogScan

Scan the the log which is implemented by a series of log files.n This log scan knows how to move across log file if it is positioned at the boundary of a log file and needs to getNextRecord.

        4 bytes - length of user data, i.e. N
        8 bytes - long representing log instant
        N bytes of supplied data
        4 bytes - length of user data, i.e. N
        

Field Summary

Fields

Modifier and Type	Field and Description
static byte	BACKWARD
static byte	BACKWARD_FROM_LOG_END
static byte	FORWARD

Constructor Summary

Constructors

Constructor and Description
Scan(LogToFile logFactory, long startAt, LogInstant stopAt, byte direction) For backward scan, we expect a scan positioned at the end of the next log record.

Method Summary

Modifier and Type	Method and Description
void	close() Close the scan.
long	getInstant() Return the log instant (as an integer) the scan is currently on - this is the log instant of the log record that was returned by getNextRecord.
LogInstant	getLogInstant() Return the log instant the scan is currently on - this is the log instant of the log record that was returned by getNextRecord.
long	getLogRecordEnd() Return the log instant at the end of the log record on the current LogFile in the form of a log instant.
LogRecord	getNextRecord(ArrayInputStream input, TransactionId tranId, int groupmask) Read the next log record.
boolean	isLogEndFuzzy() returns true if there is partially writen log records before the crash in the last log file.
void	resetPosition(LogInstant instant) Reset the scan to the given LogInstant.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

FORWARD

public static final byte FORWARD

See Also:

Constant Field Values

BACKWARD

public static final byte BACKWARD

See Also:

Constant Field Values

BACKWARD_FROM_LOG_END

public static final byte BACKWARD_FROM_LOG_END

See Also:

Constant Field Values

Constructor Detail

Scan

public Scan(LogToFile logFactory,
            long startAt,
            LogInstant stopAt,
            byte direction)
     throws java.io.IOException,
            StandardException

For backward scan, we expect a scan positioned at the end of the next log record. For forward scan, we expect a scan positioned at the beginning of the next log record. For forward flushed scan, we expect stopAt to be the instant for the first not-flushed log record. Like any forward scan, we expect a scan positioned at the beginning of the next log record.

Throws:

StandardException - Standard Derby error policy

java.io.IOException - cannot access the log at the new position.

Method Detail

getNextRecord

public LogRecord getNextRecord(ArrayInputStream input,
                               TransactionId tranId,
                               int groupmask)
                        throws StandardException

Read the next log record. Switching log to a previous log file if necessary, Resize the input stream byte array if necessary.

Specified by:

getNextRecord in interface StreamLogScan

Parameters:

input - the ArrayInputStream to put the log record

tranId - if non-null, only log record that equals tranId will be returned. If null, log records are not filtered on transaction Id.

groupmask - if non-zero, only log record whose Loggable's group value is included in the groupmask is returned. groupmask can be a bit wise OR of many Loggable groups. If zero, log records are not filtered on the Loggable's group.

Returns:

the next LogRecord, or null if the end of the scan has been reached.

Throws:

StandardException - Standard Derby error policy

See Also:

StreamLogScan.getNextRecord(org.apache.derby.iapi.services.io.ArrayInputStream, org.apache.derby.iapi.store.raw.xact.TransactionId, int)

resetPosition

public void resetPosition(LogInstant instant)
                   throws java.io.IOException,
                          StandardException

Reset the scan to the given LogInstant.

Specified by:

resetPosition in interface StreamLogScan

Parameters:

instant - the position to reset to

Throws:

java.io.IOException - scan cannot access the log at the new position.

StandardException - standard Derby error policy

getInstant

public long getInstant()

Return the log instant (as an integer) the scan is currently on - this is the log instant of the log record that was returned by getNextRecord.

Specified by:

getInstant in interface StreamLogScan

Returns:

INVALID_LOG_INSTANT if no records have been returned yet or the scan has completed.

getLogRecordEnd

public long getLogRecordEnd()

Return the log instant at the end of the log record on the current LogFile in the form of a log instant. After the scan has been closed, the end of the last log record will be returned except when the scan ended in an empty log file. In that case, the start of this empty log file will be returned. (This is done to make sure new log records are inserted into the newest log file.)

Specified by:

getLogRecordEnd in interface StreamLogScan

Returns:

INVALID_LOG_INSTANT if this is not a FORWARD scan or, no record have been returned yet or the scan has completed.

isLogEndFuzzy

public boolean isLogEndFuzzy()

returns true if there is partially writen log records before the crash in the last log file. Partiall wrires are identified during forward redo scans for log recovery.

Specified by:

isLogEndFuzzy in interface StreamLogScan

Returns:

true if fuzzy log end found during forward scan, this happens if there was a partially written log records before the crash.

getLogInstant

public LogInstant getLogInstant()

Return the log instant the scan is currently on - this is the log instant of the log record that was returned by getNextRecord.

Specified by:

getLogInstant in interface StreamLogScan

Returns:

null if no records have been returned yet or the scan has completed.

close

public void close()

Close the scan.

Specified by:

close in interface StreamLogScan