/**
* Returns the file name to use for the read-only version of the provided log file.
*
* <p>The file name is based on the lowest and highest key in the log file.
*
* @return the name to use for the read-only version of the log file
* @throws ChangelogException If an error occurs.
*/
private String generateReadOnlyFileName(final LogFile<K, V> logFile) throws ChangelogException {
final K lowestKey = logFile.getOldestRecord().getKey();
final K highestKey = logFile.getNewestRecord().getKey();
return recordParser.encodeKeyToString(lowestKey)
+ LOG_FILE_NAME_SEPARATOR
+ recordParser.encodeKeyToString(highestKey)
+ LOG_FILE_SUFFIX;
}
/**
* Find the highest key that corresponds to a record that is the oldest (or first) of a read-only
* log file and where value mapped from the record is lower or equals to provided limit value.
*
* <p>Example<br>
* Given a log with 3 log files, with Record<Int, String> and Mapper<String, Long> mapping a
* string to its long value
*
* <ul>
* <li>1_10.log where oldest record is (key=1, value="50")
* <li>11_20.log where oldest record is (key=11, value="150")
* <li>head.log where oldest record is (key=25, value="250")
* </ul>
*
* Then
*
* <ul>
* <li>findBoundaryKeyFromRecord(mapper, 20) => null
* <li>findBoundaryKeyFromRecord(mapper, 50) => 1
* <li>findBoundaryKeyFromRecord(mapper, 100) => 1
* <li>findBoundaryKeyFromRecord(mapper, 150) => 11
* <li>findBoundaryKeyFromRecord(mapper, 200) => 11
* <li>findBoundaryKeyFromRecord(mapper, 250) => 25
* <li>findBoundaryKeyFromRecord(mapper, 300) => 25
* </ul>
*
* @param <V2> Type of the value extracted from the record
* @param mapper The mapper to extract a value from a record. It is expected that extracted values
* are ordered according to an order consistent with this log ordering, i.e. for two records,
* if key(R1) > key(R2) then extractedValue(R1) > extractedValue(R2).
* @param limitValue The limit value to search for
* @return the key or {@code null} if no key corresponds
* @throws ChangelogException If a problem occurs
*/
<V2 extends Comparable<V2>> K findBoundaryKeyFromRecord(
Record.Mapper<V, V2> mapper, V2 limitValue) throws ChangelogException {
sharedLock.lock();
try {
K key = null;
for (LogFile<K, V> logFile : logFiles.values()) {
final Record<K, V> record = logFile.getOldestRecord();
final V2 oldestValue = mapper.map(record.getValue());
if (oldestValue.compareTo(limitValue) > 0) {
return key;
}
key = record.getKey();
}
return key;
} finally {
sharedLock.unlock();
}
}