Github user sachouche commented on a diff in the pull request:
https://github.com/apache/drill/pull/1072#discussion_r158074965
--- Diff:
exec/java-exec/src/main/java/org/apache/drill/exec/expr/fn/impl/SqlPatternContainsMatcher.java
---
@@ -19,44 +19,283 @@
import io.netty.buffer.DrillBuf;
-public class SqlPatternContainsMatcher extends AbstractSqlPatternMatcher {
+/** SQL Pattern Contains implementation */
+public final class SqlPatternContainsMatcher extends
AbstractSqlPatternMatcher {
+ private final MatcherFcn matcherFcn;
public SqlPatternContainsMatcher(String patternString) {
super(patternString);
+
+ // Pattern matching is 1) a CPU intensive operation and 2) pattern and
input dependent. The conclusion is
+ // that there is no single implementation that can do it all well. So,
we use multiple implementations
+ // chosen based on the pattern length.
+ if (patternLength == 1) {
+ matcherFcn = new Matcher1();
+ } else if (patternLength == 2) {
+ matcherFcn = new Matcher2();
+ } else if (patternLength == 3) {
+ matcherFcn = new Matcher3();
+ } else if (patternLength < 10) {
+ matcherFcn = new MatcherN();
+ } else {
+ matcherFcn = new BoyerMooreMatcher();
+ }
}
@Override
public int match(int start, int end, DrillBuf drillBuf) {
+ return matcherFcn.match(start, end, drillBuf);
+ }
+
+
//--------------------------------------------------------------------------
+ // Inner Data Structure
+ //
--------------------------------------------------------------------------
+
+ /** Abstract matcher class to allow us pick the most efficient
implementation */
+ private abstract class MatcherFcn {
+ protected final byte[] patternArray;
+
+ protected MatcherFcn() {
+ assert patternByteBuffer.hasArray();
+
+ patternArray = patternByteBuffer.array();
+ }
+
+ /**
+ * @return 1 if the pattern was matched; 0 otherwise
+ */
+ protected abstract int match(int start, int end, DrillBuf drillBuf);
+ }
+
+ /** Handles patterns with length one */
+ private final class Matcher1 extends MatcherFcn {
- if (patternLength == 0) { // Everything should match for null pattern
string
- return 1;
+ private Matcher1() {
+ super();
}
- final int txtLength = end - start;
+ /** {@inheritDoc} */
+ @Override
+ protected final int match(int start, int end, DrillBuf drillBuf) {
+ final int lengthToProcess = end - start;
+ final byte firstPattByte = patternArray[0];
- // no match if input string length is less than pattern length
- if (txtLength < patternLength) {
+ // simplePattern string has meta characters i.e % and _ and escape
characters removed.
+ // so, we can just directly compare.
+ for (int idx = 0; idx < lengthToProcess; idx++) {
+ byte inputByte = drillBuf.getByte(start + idx);
+
+ if (firstPattByte != inputByte) {
--- End diff --
These optimizations are useless with modern compilers. This would have been
useful if the inputByte value was the same.. then we would save few
instructions.
---
