[CWB] Computing distribution fails with uninformative error message

[Jörg Knappen]

I'm running CQPweb v3.2.31 © 2008-2018 on Ubuntu 18.04 LTS, and  
overnight "Distribution" queries started to fail with the following  
error message (I can confirm that "Distribution worked perfectly  
yesterday in the evening):

A MySQL query did not run successfully!

Original query: LOAD DATA LOCAL INFILE  
'/data2/cqpweb/cache/tab_dist_fycel9oplk' INTO TABLE  
`db_dist_g2f3ndxf40` FIELDS ESCAPED BY '' /* from User: knappen |  
Function: create_db() | 2019-Apr-25 11:23:01 */

Error # 0:


Because the error emerged overnight with nothing changed on the  
system, I suspect that some configured limit is hit, but I have no  
clue which.

Inspecting /var/log/mysql/error.log revealed nothing; and running the  
sql query directly from the mysql prompt succeeds.

What can it be?

Thanks in advance,

Jörg Knappen

P.S. PHP debugging backtrace

array(6) {
   [1]=>
   array(4) {
     ["file"]=>
     string(40) "/var/www/html/cqpweb/lib/library.inc.php"
     ["line"]=>
     int(299)
     ["function"]=>
     string(20) "exiterror_mysqlquery"
     ["args"]=>
     array(3) {
       [0]=>
       int(0)
       [1]=>
       string(0) ""
       [2]=>
       string(191) "LOAD DATA LOCAL INFILE  
'/data2/cqpweb/cache/tab_dist_fycel9oplk' INTO TABLE  
`db_dist_g2f3ndxf40` FIELDS ESCAPED BY ''
	/* from User: knappen | Function: create_db() | 2019-Apr-25 11:23:01 */"
     }
   }
   [2]=>
   array(4) {
     ["file"]=>
     string(40) "/var/www/html/cqpweb/lib/library.inc.php"
     ["line"]=>
     int(423)
     ["function"]=>
     string(14) "do_mysql_query"
     ["args"]=>
     array(1) {
       [0]=>
       &string(191) "LOAD DATA LOCAL INFILE  
'/data2/cqpweb/cache/tab_dist_fycel9oplk' INTO TABLE  
`db_dist_g2f3ndxf40` FIELDS ESCAPED BY ''
	/* from User: knappen | Function: create_db() | 2019-Apr-25 11:23:01 */"
     }
   }
   [3]=>
   array(4) {
     ["file"]=>
     string(35) "/var/www/html/cqpweb/lib/db.inc.php"
     ["line"]=>
     int(292)
     ["function"]=>
     string(21) "do_mysql_infile_query"
     ["args"]=>
     array(3) {
       [0]=>
       string(18) "db_dist_g2f3ndxf40"
       [1]=>
       string(39) "/data2/cqpweb/cache/tab_dist_fycel9oplk"
       [2]=>
       bool(true)
     }
   }
   [4]=>
   array(4) {
     ["file"]=>
     string(45) "/var/www/html/cqpweb/lib/distribution.inc.php"
     ["line"]=>
     int(81)
     ["function"]=>
     string(9) "create_db"
     ["args"]=>
     array(5) {
       [0]=>
       object(DbType)#428 (4) {
         ["type"]=>
         int(1)
         ["str"]=>
         string(4) "dist"
         ["colloc_atts"]=>
         NULL
         ["colloc_range"]=>
         NULL
       }
       [1]=>
       string(10) "fycel9oplk"
       [2]=>
       string(15) "[word="optics"]"
       [3]=>
       string(0) ""
       [4]=>
       string(0) ""
     }
   }
   [5]=>
   array(4) {
     ["file"]=>
     string(41) "/var/www/html/cqpweb/lib/redirect.inc.php"
     ["line"]=>
     int(124)
     ["args"]=>
     array(1) {
       [0]=>
       string(45) "/var/www/html/cqpweb/lib/distribution.inc.php"
     }
     ["function"]=>
     string(7) "require"
   }
   [6]=>
   array(4) {
     ["file"]=>
     string(37) "/var/www/html/cqpweb/exe/redirect.php"
     ["line"]=>
     int(1)
     ["args"]=>
     array(1) {
       [0]=>
       string(41) "/var/www/html/cqpweb/lib/redirect.inc.php"
     }
     ["function"]=>
     string(7) "require"
   }
}