[DAFFODIL-1877] Slow schema compilation due to unambiguous checks

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 2.1.0
• Component/s: Front End, Performance
• Assignee: Dave Thompson
• Reporter: Steve Lawrence
• Created: 17/Jan/18 16:40
• Updated: 22/Jan/18 12:07
• Resolved: 19/Jan/18 19:57

Description

Commit 02c8324294ed4395c1231c6ea3ec6ae77139ba46 caused ATO schema compilation time to jump from about 10 seconds to over 2 minutes. Large increases were also seen in VMF schema compilation.

Some debugging showed that the cause is likely in the DFDLPathExpressionCompiler. Wrapping the following code the compiles an individual expression in a Timer shows an average of 9000% increase in time to compile.

```scala

val compiler = new DFDLPathExpressionParser[T](qn,
nodeInfoKind, namespaces, compileInfoWherePropertyWasLocated, isEvaluatedAbove)
val compiledDPath = compiler.compile(expr)
compiledDPath

```

So this most likely has something to do with schema compilation. Nothing jumps out at me in the specified commit as being especially egregious to cause such a performance degredation. All the really changed was passing an extra parameter for error accumulation and changing how isReferencedByExpressions is set. I wouldn't expect that to cause such performance changes. Perhaps it is findNamedMatches now allocating a Seq?