managing_roll_files_directly.adoc

Managing Roll Files Directly

Table of Contents

• Chronicle FileUtil class
  • Determining if a file has a roll file suffix
  • Determining the state of a file
  • Removable roll files
  • Removable roll files via the command line

This document describes how roll files can be managed directly via Java. One example of direct management would be to remove old unused roll files.

Chronicle FileUtil class

The FileUtil class provides useful methods when managing queue files directly and is located here.

Determining if a file has a roll file suffix

The method FileUtil::hasQueueSuffix can be used to determine if a file has a roll file suffix (i.e. ".cq4"):

if (FileUtil.hasQueueSuffix(file)) {
    doStuffWithTheRollFile(file);
}

Determining the state of a file

The method FileUtil::state can be used to determine the current state of a file:

switch (FileUtil.state(file)) {
    case CLOSED: {
        processClosed(file);
        break;
    }
    case OPEN: {
        processOpen(file);
        break;
    }
    case NON_EXISTENT: {
        processNonExistent(file);
        break;
    }
    case UNDETERMINED: {
        processUndetermined(file);
        break;
    }
}

Note	The method above is only supported on Linux/BSD systems and not Windows.

Removable roll files

After some time, there might be lingering queue files that are no longer used. Identifying these files is non-trivial as there might be tailers that are still on older roll files.

For example, appenders may be on roll file 10, tailer A on file 3 and tailer B on file 5. In this case, it is only safe to remove the rolls 0, 1 and 2. In particular, roll 4 must not be removed or else tailer A will eventually fail.

The removal candidates can be identified by invoking the FileUtil::removableRollFileCandidates method as described hereunder:

List<File> candidates = FileUtil.removableRollFileCandidates(dir).collect(toList());

This will provide a new List with all candidates in the provided dir.

Note	It always the ultimate decision of the user code to actually decide if a candidate should be deleted or not.

Note	The method above is only supported on Linux/BSD systems and not Windows.

If the used code intends to remove all candidates unconditionally, the following snippet can be used:

for (File file : removableFileCandidates(baseDir).collect(Collectors.toList())) {
    if (!file.delete()) {
        break;
    }
}

Removable roll files via the command line

It is possible to obtain removable roll file candidates directly from the command line:

mvn exec:java -Dexec.mainClass="net.openhft.chronicle.queue.internal.main.InternalRemovableRollFileCandidatesMain" -Dexec.classScope=compile -Dexec.args="my_queue_dir"

This will produce a list of removable roll file candidates listed per line.

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