Map is super fragile wrt estimated sizes

[jbellis]

Documentation says that exceeding estimated size will cause rehashing; in practice it crashes like this if you exceed the estimate by more than a little

This is 3.25ea6

Caused by: java.lang.IllegalStateException: ChronicleMap{name=chunks, file=/home/jonathan/Projects/colbert-pq/chunks.dat, identityHashCode=235195640}: Attempt to allocate #2 extra segment tier, 1 is maximum.
Possible reasons include:
 - you have forgotten to configure (or configured wrong) builder.entries() number
 - same regarding other sizing Chronicle Hash configurations, most likely maxBloatFactor(), averageKeySize(), or averageValueSize()
 - keys, inserted into the ChronicleHash, are distributed suspiciously bad. This might be a DOS attack
	at net.openhft.chronicle.hash.impl.VanillaChronicleHash.allocateTier(VanillaChronicleHash.java:869)
	at net.openhft.chronicle.map.impl.CompiledMapQueryContext.nextTier(CompiledMapQueryContext.java:3115)
	at net.openhft.chronicle.map.impl.CompiledMapQueryContext.alloc(CompiledMapQueryContext.java:3476)
	at net.openhft.chronicle.map.impl.CompiledMapQueryContext.initEntryAndKey(CompiledMapQueryContext.java:3494)
	at net.openhft.chronicle.map.impl.CompiledMapQueryContext.putEntry(CompiledMapQueryContext.java:3987)
	at net.openhft.chronicle.map.impl.CompiledMapQueryContext.doInsert(CompiledMapQueryContext.java:4176)
	at net.openhft.chronicle.map.MapEntryOperations.insert(MapEntryOperations.java:153)
	at net.openhft.chronicle.map.impl.CompiledMapQueryContext.insert(CompiledMapQueryContext.java:4099)
	at net.openhft.chronicle.map.MapMethods.put(MapMethods.java:89)
	at net.openhft.chronicle.map.VanillaChronicleMap.put(VanillaChronicleMap.java:901)
	at org.example.Main.loadFile(Main.java:120)
	at org.example.Main.lambda$main$1(Main.java:64)
	at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:184)
	at java.base/java.util.AbstractList$RandomAccessSpliterator.forEachRemaining(AbstractList.java:722)
	at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:556)
	at java.base/java.util.stream.ForEachOps$ForEachTask.compute(ForEachOps.java:291)
	at java.base/java.util.concurrent.CountedCompleter.exec(CountedCompleter.java:759)
	at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:507)
	at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1491)
	at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:2073)
	at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:2035)
	at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:187)

[ryanoftalltrees]

Thanks for bringing this to our attention. The documentation is definitely misleading here. We will review it. Feel free to make a pull request yourself. It is best practice to provision your Maps to ensure that they are sized for the largest possible number of entries.

[Enixes]

I ran into this while working on TailCache as well. I’ve opened PR #625 to clarify the sizing documentation. Let me know if any of the wording needs changing or if I’ve misunderstood how the tier limit works.