1. Architecture
传统db的瓶颈在于从磁盘读写数据的性能有限。而Hana则将数据直接放置在内存中，只将logging和backup的数据存放在磁盘中，不受I/O的限制。
Sap Neatwear Abap 通过DBI (database independent layer) 访问database. DBI 中集成了open SQL 和native SQL, 默认会使用open SQL，特殊情况会使用native SQL. 基于这样的架构，在底层使用HANA DB 的时候，经典的abap performance guideline也适用于hana db的情况。
2.classical five rules
make where clause as specific as possible
use select with field list instead of select *
use aggregate functions like (count,min,max,sum,avg)
use join or sub queries instead of nested select loops
use select for all entries
use array variants of insert,update,modify,delete
define and use secondary indexes
avoid reading data redundantly
use table buffering
sort data in abap program
3.more important for sap hana
for modifying operations using array operations should be perferred to single operations
nested select loops should be avoided or replaced if possible eg.
using for all entries
using abap table buffer
