the cause of the linear slowing down was fixed

DesignNotes.wiki

@@ -171,18 +171,17 @@ and the shrunk current line, then the two lowest lines get aligned according to
 the topmost line (case 3).
 
 Performance of the newer formatting algorithm should not depend on the height
-of the table (*beware*: something still makes table editing speed linear with
-respect to its height, perhaps syntax tracking or some uncovered parts of the
-formatting algorithm). The newer algorithm should also be consistent with
-respect to user editing experience. Indeed, as soon as a table should normally
-be edited linearly, row by row, dynamic formatting should be both fast
+of the table. The newer algorithm should also be consistent with respect to
+user editing experience. Indeed, as soon as a table should normally be edited
+row by row from the top to the bottom, dynamic formatting should be both fast
 (watching only three rows in a table, re-formatting only when the shrunk
 current row gets longer than any of the two rows above) and eager (a table
-should look formatted on every pressing on _Tab_ and _Enter_). However, the
-newer algorithm differs from the older algorithm when starting editing a
-mis-aligned table in an area where mis-aligned rows do not get into the
-viewport: in this case the newer algorithm formats the table partly, in the
-rows of the viewport, while the older algorithm re-formats the whole table on
-every pressing of _Tab_ and _Enter_. In this case the whole table can be
-formatted by pressing `gqq` in the Normal mode.
+should look formatted on every press on _Tab_ and _Enter_). However, the newer
+algorithm differs from the older algorithm when starting editing a mis-aligned
+table in an area where mis-aligned rows do not get into the viewport: in this
+case the newer algorithm will format the table partly (in the rows of the
+viewport) until one of the being edited cells grows in length to a value big
+enough to trigger the older algorithm and the whole table gets aligned. When
+partial formatting is not desirable, the whole table can be formatted by
+pressing `gqq` in the Normal mode.
 

autoload/vimwiki/tbl.vim

@@ -205,7 +205,7 @@ function! s:col_count(lnum)
 endfunction
 
 
-function! s:get_indent(lnum)
+function! s:get_indent(lnum, depth)
   if !s:is_table(getline(a:lnum))
     return
   endif
@@ -220,6 +220,9 @@ function! s:get_indent(lnum)
       break
     endif
     let lnum -= 1
+    if a:depth > 0 && lnum < a:lnum - a:depth
+      break
+    endif
   endwhile
 
   return indent
@@ -272,9 +275,9 @@ function! s:get_rows(lnum, ...)
 endfunction
 
 
-function! s:get_cell_aligns(lnum)
+function! s:get_cell_aligns(lnum, depth)
   let aligns = {}
-  for [lnum, row] in s:get_rows(a:lnum)
+  for [lnum, row] in s:get_rows(a:lnum, a:depth)
   let found_separator = s:is_separator(row)
     if found_separator
       let cells = vimwiki#tbl#get_cells(row)
@@ -353,7 +356,7 @@ function! s:get_aligned_rows(lnum, col1, col2, depth)
     endfor
     let max_lens = s:get_cell_max_lens(a:lnum, cells, startlnum, rows)
   endif
-  let aligns = s:get_cell_aligns(a:lnum)
+  let aligns = s:get_cell_aligns(a:lnum, a:depth)
   let result = []
   for [lnum, row] in rows
     if s:is_separator(row)
@@ -496,8 +499,9 @@ endfunction
 function! vimwiki#tbl#goto_next_col()
   let curcol = virtcol('.')
   let lnum = line('.')
-  let newcol = s:get_indent(lnum)
-  let rows = s:get_rows(lnum, 2)
+  let depth = 2
+  let newcol = s:get_indent(lnum, depth)
+  let rows = s:get_rows(lnum, depth)
   let startlnum = rows[0][0]
   let cells = []
   for [lnum, row] in rows
@@ -530,8 +534,9 @@ endfunction
 function! vimwiki#tbl#goto_prev_col()
   let curcol = virtcol('.')
   let lnum = line('.')
-  let newcol = s:get_indent(lnum)
-  let rows = s:get_rows(lnum, 2)
+  let depth = 2
+  let newcol = s:get_indent(lnum, depth)
+  let rows = s:get_rows(lnum, depth)
   let startlnum = rows[0][0]
   let cells = []
   for [lnum, row] in rows
@@ -637,7 +642,7 @@ function! vimwiki#tbl#format(lnum, ...)
     let col2 = 0
   endif
 
-  let indent = s:get_indent(a:lnum)
+  let indent = s:get_indent(a:lnum, depth)
   if &expandtab
     let indentstring = repeat(' ', indent)
   else