MapDB is not reducing its size when all messages get deleted

[prasaddige]

1. Created MapdB, physical size of file db is 2.00 MB (2,097,152 bytes)
2. Insert 1000 messages into mapdb. Physical size of mapdb increased to 10.0 MB (10,485,760 bytes)
3. Deleted all entries from mapDB

Expected: size of DB file should go back to 2 MB
Expected: Size of DB file stays at 10.0 MB

=========================================================================
Sample code to reproduce:
public static void main(String[] args) {
File file = new File("myMapDB.db");

	DB fileDB = DBMaker.fileDB(file).closeOnJvmShutdown().make();

	HTreeMap<String, String> hTreeMap = fileDB
			.hashMap(MAP_NAME, Serializer.STRING, Serializer.STRING)
			.expireMaxSize(20000)
			.expireAfterCreate(1, TimeUnit.DAYS)
			.modificationListener(new StringRetryFileListener())
			.createOrOpen();


	System.out.println("File Size Before Insert=" + FileUtils.sizeOf(file) + ", No of Entries=" + hTreeMap.size());

	for(int i = 0; i < 1000; i++) {
		hTreeMap.put(""+i, str);
	}

	System.out.println("File Size After Insert=" + FileUtils.sizeOf(file) + ", No of Entries=" + hTreeMap.size());

	for (Entry<String, String> entry : hTreeMap.getEntries()) {
		hTreeMap.remove(entry.getKey());
	}

	System.out.println("File Size After Delete=" + FileUtils.sizeOf(file) + ", No of Entries=" + hTreeMap.size());

	System.out.println("SIZE=" + hTreeMap.size());
}

=========================================================================

Output

File Size Before Insert=2097152, No of Entries=0
File Size After Insert=10485760, No of Entries=1000
File Size After Delete=10485760, No of Entries=0

[andrm]

Try calling DB.getStore().compact()

[igalkin]

Set compaction threshold on the map creator to trigger automatic compaction when cleared space reaches certain level of the allocated space (20% in the below example):
.expireCompactThreshold(0.2)

[yoloz]

Try calling DB.getStore().compact()

Seems there is no way to that now with transaction store. #940