Bug: Improve GET_JSON_OBJECT performance on executors running multiple tasks
Status: Open | Priority: Major | Resolution: 
Created: 23/Apr/24 16:07
Affects Version/s: 3.5.1

We have a Spark executor that is running 32 workers in parallel.  The query is a simple SELECT with several `GET_JSON_OBJECT` UDF calls.

We noticed that 80+% of the stacktrace of the worker threads are blocked on the following stacktrace:

 
{code:java}
com.fasterxml.jackson.core.util.InternCache.intern(InternCache.java:50) - blocked on java.lang.Object@7529fde1 com.fasterxml.jackson.core.sym.ByteQuadsCanonicalizer.addName(ByteQuadsCanonicalizer.java:947) com.fasterxml.jackson.core.json.UTF8StreamJsonParser.addName(UTF8StreamJsonParser.java:2482) com.fasterxml.jackson.core.json.UTF8StreamJsonParser.findName(UTF8StreamJsonParser.java:2339) com.fasterxml.jackson.core.json.UTF8StreamJsonParser.parseMediumName(UTF8StreamJsonParser.java:1870) com.fasterxml.jackson.core.json.UTF8StreamJsonParser._parseName(UTF8StreamJsonParser.java:1825) com.fasterxml.jackson.core.json.UTF8StreamJsonParser.nextToken(UTF8StreamJsonParser.java:798) com.fasterxml.jackson.core.base.ParserMinimalBase.skipChildren(ParserMinimalBase.java:240) org.apache.spark.sql.catalyst.expressions.GetJsonObjectBase.evaluatePath(jsonExpressions.scala:383) org.apache.spark.sql.catalyst.expressions.GetJsonObjectBase.evaluatePath(jsonExpressions.scala:287) org.apache.spark.sql.catalyst.expressions.GetJsonObjectBase.$anonfun$eval$4(jsonExpressions.scala:198) org.apache.spark.sql.catalyst.expressions.GetJsonObjectBase.$anonfun$eval$4$adapted(jsonExpressions.scala:196) org.apache.spark.sql.catalyst.expressions.GetJsonObjectBase$$Lambda$8585/1316745697.apply(Unknown Source)
...
{code}
 

Apparently jackson-core has such a performance bug from version 2.3 - 2.15, and not fixed until version 2.18 (unreleased): [https://github.com/FasterXML/jackson-core/blob/fc51d1e13f4ba62a25a739f26be9e05aaad88c3e/src/main/java/com/fasterxml/jackson/core/util/InternCache.java#L50] 
{code:java}
            synchronized (lock) {
                if (size() >= MAX_ENTRIES) {
                    clear();
                }
            }
{code}
 
instead of [https://github.com/FasterXML/jackson-core/blob/8b87cc1a96f649a7e7872c5baa8cf97909cabf6b/src/main/java/com/fasterxml/jackson/core/util/InternCache.java#L59] 
{code:java}
            /* As of 2.18, the limit is not strictly enforced, but we do try to
             * clear entries if we have reached the limit. We do not expect to
             * go too much over the limit, and if we do, it's not a huge problem.
             * If some other thread has the lock, we will not clear but the lock should
             * not be held for long, so another thread should be able to clear in the near future.
             */
            if (lock.tryLock()) {
                try {
                    if (size() >= DEFAULT_MAX_ENTRIES) {
                        clear();
                    }
                } finally {
                    lock.unlock();
                }
            }   {code}
 

Potential fixes:
 # Upgrade to Jackson-core 2.18 when it's released;
 # Follow [https://github.com/FasterXML/jackson-core/issues/998] - I don't totally understand the options suggested by this thread yet.
 # Introduce a new UDF that doesn't depend on jackson-core