/util
appendToTable:{[tableHandle;numberOfRows]
  V:"abcdefghijklmnopqrstuvwxyz" / universe of values
  e:numberOfRows?1000000000 / 1 billion possible entities
  v:numberOfRows?V / select #rows value
  t:numberOfRows#1+last get[tableHandle]@`t / next transaction id
  .[tableHandle;();,;flip`e`v`t!(e;v;t)]
  :e}
  
/ setup
n:14 / 1,2,3,4,6,8,12,14 yield 676,169,81,49,25,16,9,4 combinations, respectively
tableHandles:`$(":db/",/:raze T,\:/:T:cut[n;"abcdefghijklmnopqrstuvwxyz"]),'"/"

/ run
set[;([] e:`long$(); v:`char$(); t:`long$())] each tableHandles
appendToTable[;1000000] each tableHandles
appendToTable[;10] each tableHandles

/ RESULTS in MBP with 16 GB, 2.6 GHz Intel Core i7 and SSD:

/ 169 Tables
/ 169 million rows appended in 22 seg. total 2.88 GB (169 tables, 1 million each)
/ after that, 10 rows are appended to all 169 tables in 50-200 ms

/ 25 Tables
/ 25 million rows appended in 3.7 seg. total 400MB (25 tables, 1 million each)
/ after that, 10 rows are appended to all 25 tables in ~25ms

/ 9 Tables
/ 9 million rows appended in 1.5 seg. total 140MB (9 tables, 1 million each)
/ after that, 10 rows are appended to all 9 tables in ~8ms