所以我创建了一个像这样工作的数据库：
static class Record implements Serializable
{
final String action;
final String categoryOfAction;
final String personWhoPerformedAction;
final Long timeOfOccurrence;
public record(String actn, String cat, String person, Long time)
{
action = actn;
categoryOfAction = cat;
personWhoPerformedAction = person;
timeOfOccurence = time;
}
}
static void main(String[] args)
{
DB thedb = DBMaker.newFileDB(new File("D:\\thedb.db")
.compressionEnable()
.closeOnJvmShutdown()
.mmapFileEnableIfSupported()
.transactionDisable()
.asyncWriteEnable()
.make();
//primaryMap maps each record to a unique ID
BTreeMap<Integer,Record> primaryMap = thedb.createTreeMap("pri")
.keySerializer(BTreeKeySerializer.INTEGER)
.makeOrGet();;
//this map holds the unique ID of every record in primaryMap with a common action
NavigableSet<Object[]> map_commonAction = thedb.createTreeSet("com_a")
.comparator(Fun.COMPARABLE_ARRAY_COMPARATOR)
.makeOrGet();
//this map holds the unique ID of every record in primaryMap with a common person
NavigableSet<Object[]> map_commonPerson = thedb.createTreeSet("com_p")
.comparator(Fun.COMPARABLE_ARRAY_COMPARATOR)
.makeOrGet();
//binding map_commonAction to primaryMap so it is updated with primary
Bind.secondaryKey(primaryMap, map_commonAction, new Fun.Function2<String, Integer, Record>() {
@Override
public String run(Integer recordID, Record r) {
return r.action;
}
});
//binding map_commonPerson to primaryMap so it is updated with primary
Bind.secondaryKey(primaryMap, map_commonPerson, new Fun.Function2<String, Integer, Record>() {
@Override
public String run(Integer recordID, Record r) {
return r.personWhoPerformedAction;
}
});
//method used to attain all records with some action
for (Object[] k : Fun.filter(map_commonAction, "someAction"))
{
Record obtainedRecord = primary.get(k[1]);
}
//method used to attain all records with some person
for (Object[] k : Fun.filter(map_commonPerson, "somePerson"))
{
Record obtainedRecord = primary.get(k[1]);
}
}
创建之后，我插入了190亿件物品。通过某些动作或人获得所有记录的方法完美地工作。我关闭了数据库，然后我再次尝试运行它，除了这次数据库已经构建并插入了所有项目，因此无需插入190亿个项目。一旦我通过一些动作或人员调用了获取所有记录的方法之一，我就会收到此错误：
Exception in thread "main" java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to java.lang.Comparable
at org.mapdb.Fun$1.compare(Fun.java:31)
at org.mapdb.BTreeKeySerializer$BasicKeySerializer.compare(BTreeKeySerializer.java:206)
at org.mapdb.BTreeKeySerializer$BasicKeySerializer.compare(BTreeKeySerializer.java:156)
at org.mapdb.BTreeKeySerializer.compareIsSmaller(BTreeKeySerializer.java:48)
at org.mapdb.BTreeKeySerializer.findChildren(BTreeKeySerializer.java:89)
at org.mapdb.BTreeMap.nextDir(BTreeMap.java:843)
at org.mapdb.BTreeMap.findLargerNode(BTreeMap.java:1673)
at org.mapdb.BTreeMap$BTreeIterator.<init>(BTreeMap.java:1068)
at org.mapdb.BTreeMap$BTreeKeyIterator.<init>(BTreeMap.java:1323)
at org.mapdb.BTreeMap$SubMap.keyIterator(BTreeMap.java:2483)
at org.mapdb.BTreeMap$KeySet.iterator(BTreeMap.java:1900)
at org.mapdb.Fun$12.iterator(Fun.java:369)
at test.main(test.java:187)
然后检查每张地图的大小
System.out.println(map_commonAction.size()); //returned correct size: 19billion
System.out.println(map_commonPerson.size()); //returned correct size: 19billion
System.out.println(primaryMap.size()); //returned correct size: 19billion
然后我检查了primaryMap是否工作，并检查了几个int值，它返回了一个像它应该的记录
Record r1 = primaryMap.get(1);
Record r2 = primaryMap.get(2);
System.out.println(r1.toString());
System.out.println(r2.toString());
当我尝试迭代Fun.filter给出的内容时，它只会失败（map_common *，＆＃34;某些东西＆＃34;）但调用它的行为不会使它失败，只是试图迭代它。我测试它是这样的：
//this method fails and causes and exception to be thrown
for (Object[] k : Fun.filter(map_commonPerson, "person"))
{
System.out.println(primaryMap.get(k[1]).toString());
}
//this method doesn't cause an exception to be thrown
Iterable<Object[]> x = Fun.filter(map_commonPerson, "person");
所以现在我被卡住了，我不知道我的地图有什么问题。一旦我创建了一个新数据库并插入了190亿个项目，它就能完美运行，但是一旦我关闭它并尝试重新打开它以获得更多阅读它就会失败。
有人可以帮忙吗？感谢。
答案 0 :(得分：3)
我找到了一个解决方案，它涉及将map_commonPerson和map_commonAction组合到同一个地图中，并使用Bind.secondaryKeys（）代替Bind.secondaryKey（）函数。为什么是这样？每个地图只能安装一个修改监听器吗？
这里是关闭后正确恢复的工作DB的代码：
static class Record implements Serializable
{
final String action;
final String categoryOfAction;
final String personWhoPerformedAction;
final Long timeOfOccurrence;
public record(String actn, String cat, String person, Long time)
{
action = actn;
categoryOfAction = cat;
personWhoPerformedAction = person;
timeOfOccurence = time;
}
}
static void main(String[] args)
{
DB thedb = DBMaker.newFileDB(new File("D:\\thedb.db")
.compressionEnable()
.closeOnJvmShutdown()
.mmapFileEnableIfSupported()
.transactionDisable()
.asyncWriteEnable()
.make();
//primaryMap maps each record to a unique ID
BTreeMap<Integer,Record> primaryMap = thedb.createTreeMap("pri")
.keySerializer(BTreeKeySerializer.INTEGER)
.makeOrGet();;
//this map holds the unique ID of every record with the same person or action
NavigableSet<Object[]> map_commonAttributes = thedb.createTreeSet("com_a")
.comparator(Fun.COMPARABLE_ARRAY_COMPARATOR)
.makeOrGet();
//binding map_commonAction to primaryMap so it is updated with primary
Bind.secondaryKeys(primaryMap, map_commonAttributes, new Fun.Function2<String[], Integer, Record>() {
@Override
public String[] run(Integer recordID, Record r) {
return new String[]{record.action, record.personWhoPerformedAction};
}
});
//method used to attain all records with same person or action
for (Object[] k : Fun.filter(map_commonAttribute, "somePersonOrAction"))
{
Record obtainedRecord = primary.get(k[1]);
}