Question

I need count rows in table. So I use reg. exp. extractor. But response assertion ends with error and tried to find exactly rows:${ROWS_matchnr}.

I tried google, but I only find a few non-functional recommendations.

Thread Group
    Http Cookie Manager
    Http Request
        Regular Expression Extractor(ROWS, row-(.*), $1$, 0, )
        Response Assertion(rows:${ROWS_matchnr})

Answer 1

Change the value you have in the Match No field from 0 to -1. As documented in the, ahem, useless official help:

If the match number is set to a negative number, then all the possible matches in the sampler data are processed. The variables are set as follows:

   refName_matchNr - the number of matches found; could be 0
   refName_n, where n = 1,2,3 etc - the strings as generated by the template
   refName_n_gm, where m=0,1,2 - the groups for match n
   refName - always set to the default value
   refName_gn - not set

Then change ${ROWS_matchnr} to ${ROWS_matchNr} (capital N) and it should work.

If you still have issues then use a Debug Sampler to see what is getting returned from the regex.