cap memory table size as maxMemTableSize-1

[ucwong]

No description provided.

[codecov]

Codecov Report

Merging #1786 (4424903) into master (988f1f4) will increase coverage by 0.04%.
Report is 355 commits behind head on master.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #1786      +/-   ##
==========================================
+ Coverage   52.68%   52.73%   +0.04%     
==========================================
  Files         485      485              
  Lines       60519    60519              
==========================================
+ Hits        31885    31914      +29     
+ Misses      26183    26148      -35     
- Partials     2451     2457       +6     

Files	Coverage Δ
ctxcdb/pebble/pebble.go	37.50% <0.00%> (ø)

... and 15 files with indirect coverage changes