doom369 commented on code in PR #14920:
URL: https://github.com/apache/lucene/pull/14920#discussion_r2192873292
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lucene/core/src/java/org/apache/lucene/index/IndexFileNames.java:
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@@ -145,14 +145,28 @@ public static String stripSegmentName(String filename) {
/** Returns the generation from this file name, or 0 if there is no
generation. */
public static long parseGeneration(String filename) {
assert filename.startsWith("_");
- String[] parts = stripExtension(filename).substring(1).split("_");
+ int dot = filename.indexOf('.');
+ int end = (dot != -1) ? dot : filename.length();
+ int start = 1; // skip initial '_'
+
+ int first = filename.indexOf('_', start);
+ if (first == -1 || first >= end) {
+ return 0;
+ }
+
+ int second = filename.indexOf('_', first + 1);
+ int third = (second != -1) ? filename.indexOf('_', second + 1) : -1;
+
+ int parts = (second == -1 || second >= end) ? 2 : (third == -1 || third >=
end) ? 3 : 4;
+
Review Comment:
In our scenario, index updates (and we have ~6 different indexes) can happen
every 5 seconds. It's profiling info from a 5-minute production run with a
async-profiler (one of the best at the moment, imho). So, if these allocations
were captured, they're not rare. Agree about complexity. But this method now
should be also 5-10x faster if that matters for you. If you want, I can provide
you with a microbenchmark.
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