oracle hint
nocache
1,/*+ nocache(table) */
2,如果一个表进行全表扫描把这它放在buffer cache的lru(least recently used),这样就可以快速为其它更需要buffer cache的块free space
3,cache与nocache会影响v$sysstat有关table scan(long tables)和table scans(short tables)的统计值
4,347 long table scan,348 short table scan
5,每次添加cache运行后,348的值增加5,为何是加5而不是其它的值呢
添加nocache也同理,为何
SQL> select /*+ cache(t_append) */ a from t_append;

         A
----------
         1
         1
         1

SQL> select * from v$sesstat where sid=70 and statistic# in(347,348);

       SID STATISTIC#      VALUE
---------- ---------- ----------
        70        347         85
        70        348         15

SQL> select /*+ cache(t_append) */ a from t_append;

         A
----------
         1
         1
         1

SQL> select * from v$sesstat where sid=70 and statistic# in(347,348);

       SID STATISTIC#      VALUE
---------- ---------- ----------
        70        347         85
        70        348         20

SQL>

SQL> select * from v$sesstat where sid=70 and statistic# in(347,348);

       SID STATISTIC#      VALUE
---------- ---------- ----------
        70        347         86
        70        348         30

SQL> select /*+ nocache(t_append) */ a from t_append;

         A
----------
         1
         1
         1

SQL> select * from v$sesstat where sid=70 and statistic# in(347,348);

       SID STATISTIC#      VALUE
---------- ---------- ----------
        70        347         86
        70        348         35

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oracle hint_cache_nocache

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