doom369 commented on code in PR #14920:
URL: https://github.com/apache/lucene/pull/14920#discussion_r2192873292
##########
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 marker 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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