Query went slow all of sudden. ON V 11.3

Hi All,

All of sudden the query went slow before the query was executing in 30- 35
sec now even after 30 mins i am not getting any result.

later I have dropped a table ( t_meners) and recreated it and again it
started working very fast.

is there way to find what happen on that why is not any issue in table how
to find out. i Have the same issue on the other databases also so that i
can check on it

SELECT ((UID-1)/10000) AS BatchNo,
* INTO "temp_tt1"
FROM
(SELECT ROW_NUMBER() OVER (
ORDER BY a."rno") AS UID,
a.*
FROM "temp_10032019020721_4470" AS a
INNER JOIN "t_ages" AS b ON LOWER(a."cr") = LOWER(b."c_pagealias")
LEFT JOIN "t_meners" AS c ON LOWER(a."cr") = LOWER(c."c_id")
WHERE c."c_id" IS NULL ) AS TempTable