Hi Thomas,
Thank you for your answer.
Yes, I am using MVStore.cache.
The MVStore object is instantiated like this:
store = MVStore.open(file.getPath());
store.setAutoCommitDelay(0);
store.setReuseSpace(true);
store.setVersionsToKeep(0);
store.setCacheSize(descriptor.getCacheSizeMb());
I investigated the cache miss problem more detailed and it turned out that
it is caused by an unstable calculation of used cache size in MVStore.
Depending on the situation A. and B. (see below) different cache size is
returned by method store.getCache().getUsedMemory().
A.) An empty data file is opened with MVStore and a new dataset is imported
(put ~ 1 million entries in different MVMaps). Then a search function is
executed against the dataset (MVMap.get operations). During search, cache
hits=1.1 million, cache misses=0, cache size=1336MB. (value reported by
store.getCache().getUsedMemory() / 1024 / 1024)
B.) Close MVStore and reopen using data file created and written to disk in
case A. Run same search function as in case A. The first run loads caches,
so subsequent runs are faster. During search, cache hits=1.1 million, cache
misses=0,
*cache size=5032MB.*Data stored in MVStore in both cases A, B are the same
and the same search function is executed. Cache miss is zero in both
cases. Used cache size calculation of MVStore is still very different in
these cases. How is it possible? Do you think we found a bug? Or some more
special configuration on caching should be done?
If a maximum cache size of (for example) 3000MB is set up then all needed
map entries are cached in case A. but only a part of them are cached in
case B. This difference in cache misses is reflected also in highly
increased execution time of the search function in case B.
Another anomaly: In case B. when used cache size is reported to be 5032Mb,
the whole java process allocates only 1.7GB of memory. Consequently it is
impossible to cache ~5G of data. Used cache size calculation seems to be
incorrect. This incorrect calculation prohibits proper cache size
configuration.
Each versions: 1.4.193, 1.4.180 and 1.3.175 has this behavior.
Java: Oracle JDK 1.8.0_121 on Linux 64bit
Thanks for any help.
Regards, Roland
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