Enhancements:

• Performance optimization for select count(*)
• Optimization about Performance scalability for STMT inserting

Fixed Bugs:

• taosd can't start after being stopped forced during high stress writing
• taosd can't be restarted after crashing
• tasod crash when creating 200 million tables and can't restart
• taosd OOM when querying the number of subtables in parallel with creating subtables
• taosdump crash when exporting data
• taosBenchmark crash during high stress writing
• Calculation error in SUM() function
• Error "Table not exists" after dropping database
• "Show create table" command can't show the comment
• A few other crash problems in taosd
• A few memory leak problems in taosd