Ticker and Histogram enumeration types out of sync with Java API

[bentorfs]

Problem: The enumerations of tickers and histogram types for retrieving statistics are not in sync between the C++ source and the java API:

Java version:
https:/facebook/rocksdb/blob/master/java/src/main/java/org/rocksdb/TickerType.java
https:/facebook/rocksdb/blob/master/java/src/main/java/org/rocksdb/HistogramType.java
C++ version:
https:/facebook/rocksdb/blob/master/include/rocksdb/statistics.h

The java Enumeration is missing a lot of declarations, and their values do not correspond to the (implicit) order of values in the C++ enum.

Impact: for example, retrieving the BLOOM_FILTER_USEFUL statistic through the java API, actually returns the data for BLOCK_CACHE_FILTER_MISS.

[lightmark]

Yes. Since we are short of ppl maintaining Java api, would you like to contribute?

[koldat]

@adamretter I was facing same issue. In this case I would recommend to use portable (maybe slower) way (strings over numbers). I made a change in this way in our local repo using TickersNameMap. It works perfectly and does not require to maintain the enumerations at all. What do you think?

[adamretter]

@koldat Is it possible to see an example?

[koldat]

@adamretter Roughly like this:

Statistics.java:

  private static ConcurrentMap<String, Integer> tickerCache = new ConcurrentHashMap<>();
  
  // Returns -1 is mapping not found
  private native int getTickerId0(String tickerType, long handle);
  
  // Returns -1 is mapping not found
  public long getTickerCount(String tickerType) {
    assert(isInitialized());
      
    Integer type = tickerCache.get(tickerType);
    if (type == null) {
      type = getTickerId0(tickerType, statsHandle_);
      tickerCache.put(tickerType, type);
    }
    if (type == -1) {
        return -1;
    }
      
    return getTickerCount0(type, statsHandle_);
  }

// The same for histograms

And enumeration can reference strings. For missing enum one can still use string without library change.

[adamretter]

@koldat Sorry I can't understand what you mean from the above code, I don't see any enums involved there.

[koldat]

@adamretter That is actual usage. Enum can be:

public enum TickerType {
  // total block cache misses
  // REQUIRES: BLOCK_CACHE_MISS == BLOCK_CACHE_INDEX_MISS +
  //                               BLOCK_CACHE_FILTER_MISS +
  //                               BLOCK_CACHE_DATA_MISS;
  BLOCK_CACHE_MISS("rocksdb.block.cache.miss");
  // total block cache hit
  // REQUIRES: BLOCK_CACHE_HIT == BLOCK_CACHE_INDEX_HIT +
  //                              BLOCK_CACHE_FILTER_HIT +
  //                              BLOCK_CACHE_DATA_HIT;

  private final String value_;

  private TickerType(String value) {
    value_ = value;
  }

  public String getValue() {
    return value_;
  }
}

There are more use cases:

1. C++ untroduces new ticker not maintained in enum. You can still query for it.
2. You can use bulk query to retireve all tickers as map<String, Long> values. Regardless on enum. We have for example monitoring solution that consume string -> value map.

[koldat]

@adamretter What do you think? Should I go ahead and create pull request?

[gfosco]

Closing this via automation due to lack of activity. If discussion is still needed here, please re-open or create a new/updated issue.