sphinx search: how to understand min_prefix_len

Question

Sorry I post my question here as I permanently get an error on the sphinxsearch forum where it belongs to.

I have set min_prefix_len = 3.

According to http://sphinxsearch.com/docs/current/conf-min-prefix-len.html I expect a match for

val*

but I do not even get a match for

vale*

however I get all matches for

valeg*
valegr*
valegro*

What is it that I do not understand?

Answer 1

I'm sorry, now it works like it should. Possible explanation is an error in the index. While exploring manticore as an alternative to sphinx, I reindexed and by chance noticed that rotation did not occur although the indexer said so:

rotating indices: successfully sent SIGHUP to searchd (pid=8).

But looking at the disk proved that this was not the case:

# ls -latrh /d/data/sphinx/*sm_en*
-rw-r--r-- 1 root root    0 Jul 29 04:43 /d/data/sphinx/lng_sm_en.spm
-rw-r--r-- 1 root root  31K Jul 29 04:43 /d/data/sphinx/lng_sm_en.spa
-rw-r--r-- 1 root root    0 Jul 29 04:43 /d/data/sphinx/lng_sm_en.spk
-rw-r--r-- 1 root root 607K Jul 29 04:43 /d/data/sphinx/lng_sm_en.spi
-rw-r--r-- 1 root root 5.7M Jul 29 04:43 /d/data/sphinx/lng_sm_en.spd
-rw-r--r-- 1 root root  11M Jul 29 04:43 /d/data/sphinx/lng_sm_en.spp
-rw-r--r-- 1 root root  30M Jul 29 04:43 /d/data/sphinx/lng_sm_en.sps
-rw-r--r-- 1 root root  823 Jul 29 04:43 /d/data/sphinx/lng_sm_en.sph
-rw-r--r-- 1 root root  38K Jul 29 04:43 /d/data/sphinx/lng_sm_en.spe
-rw------- 1 root root    0 Jul 29 04:43 /d/data/sphinx/lng_sm_en.spl
-rw-r--r-- 1 root root    0 Jul 31 00:36 /d/data/sphinx/lng_sm_en.new.spm
-rw-r--r-- 1 root root  31K Jul 31 00:36 /d/data/sphinx/lng_sm_en.new.spa
-rw-r--r-- 1 root root    0 Jul 31 00:36 /d/data/sphinx/lng_sm_en.new.spk
-rw-r--r-- 1 root root  11M Jul 31 00:36 /d/data/sphinx/lng_sm_en.new.spp
-rw-r--r-- 1 root root 607K Jul 31 00:36 /d/data/sphinx/lng_sm_en.new.spi
-rw-r--r-- 1 root root 5.7M Jul 31 00:36 /d/data/sphinx/lng_sm_en.new.spd
-rw-r--r-- 1 root root  823 Jul 31 00:36 /d/data/sphinx/lng_sm_en.new.sph
-rw-r--r-- 1 root root  30M Jul 31 00:36 /d/data/sphinx/lng_sm_en.new.sps
-rw-r--r-- 1 root root  38K Jul 31 00:36 /d/data/sphinx/lng_sm_en.new.spe
-rw------- 1 root root    0 Jul 31 00:36 /d/data/sphinx/lng_sm_en.new.spl

So I deleted these files and indexed again. Probably this fixed the issue, as rotating works again as well.

As the filedates show, this problem must have been lingering for 2 weeks. Now the dates are correct, too.