Who so much "db block gets" in Oracle 8i?

From: AnySQL (d.c.b.a) <anysql_at_gmail.com>
Date: 16 May 2005 22:22:13 -0700
Message-ID: <1116307333.188518.183780@g47g2000cwa.googlegroups.com>

I opened two session, one to query data, and one to query v$sesstat to monitor session one's statistics, and I set the arraysize to 1 in session one, and got the following result:

Session 2
SQL> SELECT STATISTIC#,NAME FROM V$STATNAME WHERE STATISTIC# IN (38,39);

STATISTIC# NAME

        38 db block gets
        39 consistent gets

Session 2
SQL> SELECT STATISTIC#,VALUE FROM V$SESSTAT WHERE STATISTIC# IN (38,39) AND SID=12; STATISTIC# VALUE
---------- ----------

        38        266
        39        991

Session 1
SQL> SELECT * FROM T1;

TNAME                          TABTYPE  CLUSTERID


------------------------------ ------- ----------

T1                             TABLE
TAB_CPU_STATS                  TABLE
TAB_DISK_STATS                 TABLE
TAB_KERNEL_STATS               TABLE
TAB_LOGIN_STATS                TABLE
TAB_MEM_STATS                  TABLE
TAB_MOUNT_STATS                TABLE
TAB_PROCESS_STATS              TABLE
TAB_SWAP_STATS                 TABLE
TAB_TS_STATS                   TABLE

10 rows selected.

Session 2
SQL> SELECT STATISTIC#,VALUE FROM V$SESSTAT WHERE STATISTIC# IN (38,39) AND SID=12; STATISTIC# VALUE
---------- ----------

        38        278
        39       1001

I want to know that why there are 12 "db block gets", it should be zero a a very small number to access the segment header block. Received on Tue May 17 2005 - 00:22:13 CDT