[HDFS-5541] LIBHDFS questions and performance suggestions

• Type: Improvement
• Status: Resolved
• Priority: Minor
• Resolution: Invalid
• Component/s: hdfs-client
• Assignee: Unassigned
• Reporter: Stephen Bovy
• Created: 21/Nov/13 03:23
• Updated: 07/Dec/13 06:29
• Resolved: 07/Dec/13 06:29

Description

Since libhdfs is a "client" interface", and esspecially because it is a "C" interface , it should be assumed that the code will be used accross many different platforms, and many different compilers.

1) The code should be cross platform ( no Linux extras )
2) The code should compile on standard c89 compilers, the
>>>

{least common denominator rule applies here}

!! <<

C code with "c" extension should follow the rules of the c standard

All variables must be declared at the begining of scope , and no (//) comments allowed

>> I just spent a week white-washing the code back to nornal C standards so that it could compile and build accross a wide range of platforms <<

Now on-to performance questions

1) If threads are not used why do a thread attach ( when threads are not used all the thread attach nonesense is a waste of time and a performance killer )

2) The JVM init code should not be imbedded within the context of every function call . The JVM init code should be in a stand-alone LIBINIT function that is only invoked once. The JVM * and the JNI * should be global variables for use when no threads are utilized.

3) When threads are utilized the attach fucntion can use the GLOBAL jvm * created by the LIBINIT

{ WHICH IS INVOKED ONLY ONCE }

and thus safely outside the scope of any LOOP that is using the functions

4) Hash Table and Locking Why ?????
When threads are used the hash table locking is going to hurt perfromance . Why not use thread local storage for the hash table,that way no locking is required either with or without threads.

5) FINALLY Windows Compatibility

Do not use posix features if they cannot easilly be replaced on other platforms !!

Issue Links

• is related to: HDFS-5643 libhdfs AIX compatibility.
• is related to: HDFS-5644 Reduce lock contention in libhdfs global class reference hash table
• is related to: HDFS-5642 libhdfs Windows compatibility.