Text Index. Make MIN_WORD_PREFIX_SIZE configurable.

[aindlq]

Default value of MIN_WORD_PREFIX_SIZE is 4, which can be a bit too high for some searches. Is it possible to make it configurable? Would it work if I just change it to 3? It says here https://github.com/ad-freiburg/qlever/blob/14d6e1cc26b53f2ff563e98fcee57135df3537bb/src/index/IndexImpl.Text.cpp#L482:

If you need this to be changed, please contact the developers

[hannahbast]

@aindlq Can you tell us how large your text corpus is, that is, how many word occurrences? And yes, as a very first step this should be configurable.

[aindlq]

Right now it is:

INFO: Statistics for text index: #words = 10,714,805, #blocks = 42,960

That is only a subset of the whole data that we are going to load. I guess in the end it should be x5-10 from that number

[hannahbast]

@aindlq Have you tried just lowering the value? For 10M words, even MIN_WORD_PREFIX_SIZE = 1 should be fine. For 100M words, MIN_WORD_PREFIX_SIZE = 2 might still be OK.

[aindlq]

@hannahbast seems to be working fine with MIN_WORD_PREFIX_SIZE = 3 , with a minor change to:

static cppcoro::generator<std::string> fourLetterPrefixes() {
....
  for (char a : chars()) {
    for (char b : chars()) {
      for (char c : chars()) {
          std::string s{a, b, c};
          co_yield s;
      }
    }
  }
}