[LUCENE-7525] ASCIIFoldingFilter.foldToASCII performance issue due to large compiled method size

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 6.2.1
• Component/s: modules/analysis
• Lucene Fields: New
• Assignee: Unassigned
• Reporter: Karl von Randow
• Created: 27/Oct/16 05:13
• Updated: 28/Aug/22 15:05

Description

The ASCIIFoldingFilter.foldToASCII method has an enormous switch statement and is too large for the HotSpot compiler to compile; causing a performance problem.

The method is about 13K compiled, versus the 8KB HotSpot limit. So splitting the method in half works around the problem.

In my tests splitting the method in half resulted in a 5X performance increase.

In the test code below you can see how slow the fold method is, even when it is using the shortcut when the character is less than 0x80, compared to an inline implementation of the same shortcut.

So a workaround is to split the method. I'm happy to provide a patch. It's a hack, of course. Perhaps using the MappingCharFilterFactory with an input file as per SOLR-2013 would be a better replacement for this method in this class?

public class ASCIIFoldingFilterPerformanceTest {

	private static final int ITERATIONS = 1_000_000;

	@Test
	public void testFoldShortString() {
		char[] input = "testing".toCharArray();
		char[] output = new char[input.length * 4];

		for (int i = 0; i < ITERATIONS; i++) {
			ASCIIFoldingFilter.foldToASCII(input, 0, output, 0, input.length);
		}
	}

	@Test
	public void testFoldShortAccentedString() {
		char[] input = "éúéúøßüäéúéúøßüä".toCharArray();
		char[] output = new char[input.length * 4];

		for (int i = 0; i < ITERATIONS; i++) {
			ASCIIFoldingFilter.foldToASCII(input, 0, output, 0, input.length);
		}
	}

	@Test
	public void testManualFoldTinyString() {
		char[] input = "t".toCharArray();
		char[] output = new char[input.length * 4];

		for (int i = 0; i < ITERATIONS; i++) {
			int k = 0;
			for (int j = 0; j < 1; ++j) {
				final char c = input[j];
				if (c < '\u0080') {
					output[k++] = c;
				} else {
					Assert.assertTrue(false);
				}
			}
		}
	}
}