我如何知道Oracle中的表是否碎片化？

如何解决我如何知道Oracle中的表是否碎片化？

| 我有一张桌子似乎占用了过多的空间。建议我将数据复制到新表，然后重命名新表和旧表以交换它们。如何确认当前表是否实际为碎片？如何估算或计算包含相同数据的新表的新大小？

解决方法

如果您的统计信息是最新的，那么如果表中的块多于行数据的数量，这应该可以很好地表明。

select table_name,round((num_rows * avg_row_len) /(8*1024)),blocks 
from user_tables where ....

该空间将用于将来的插入，因此不一定是问题。如果您已完成大型数据存档或删除，则可能值得回收空间（特别是如果您进行大量全表扫描）。 [注意：我假设是8k块，这是默认值。] 如果执行CREATE / DROP / RENAME，则会丢失所有索引，约束，授权（如果使用它们，还会加上表注释）。最好检查当前表空间（在USER_SEGMENTS中查看）并执行ALTER TABLE tablename MOVE current_tablespace; 您也将需要在后端重建索引。从USER_INDEXES挑选它们，然后做ALTER INDEX ... REBUILD; , -尝试使用以DBA连接的svrmgrl运行此脚本

set serveroutput on

DECLARE
   libcac   NUMBER (6,2);
   rowcac   NUMBER (6,2);
   bufcac   NUMBER (6,2);
   redlog   NUMBER (6,2);
   spsize   NUMBER;
   blkbuf   NUMBER;
   logbuf   NUMBER;
BEGIN
   SELECT VALUE
     INTO redlog
     FROM v$sysstat
    WHERE name = \'redo log space requests\';

   SELECT 100 * (SUM (pins) - SUM (reloads)) / SUM (pins)
     INTO libcac
     FROM v$librarycache;

   SELECT 100 * (SUM (gets) - SUM (getmisses)) / SUM (gets)
     INTO rowcac
     FROM v$rowcache;

   SELECT 100 * (cur.VALUE con.VALUE - phys.VALUE)/(cur.VALUE con.VALUE)
into bufcac
from v$sysstat cur,v$sysstat con,v$sysstat phys,v$statname ncu,v$statname nco,v$statname nph
where cur.statistic# = ncu.statistic# and
ncu.name = \'db block gets\' and
con.statistic# = nco.statistic# and
nco.name = \'consistent gets\' and
phys.statistic# = nph.statistic# and
nph.name = \'physical reads\';

select VALUE
into spsize
from v$parameter
where name = \'shared_pool_size\';

select VALUE
into blkbuf
from v$parameter
where name = \'db_block_buffers\';

select VALUE
into logbuf
from v$parameter
where name = \'log_buffer\';

DBMS_OUTPUT.put_line(\'> SGA CACHE STATISTICS\');
DBMS_OUTPUT.put_line(\'> ********************\');
DBMS_OUTPUT.put_line(\'> SQL Cache Hit rate = \'||libcac);
DBMS_OUTPUT.put_line(\'> Dict Cache Hit rate = \'||rowcac);
DBMS_OUTPUT.put_line(\'> Buffer Cache Hit rate = \'||bufcac);
DBMS_OUTPUT.put_line(\'> Redo Log space requests = \'||redlog);
DBMS_OUTPUT.put_line(\'> \');
DBMS_OUTPUT.put_line(\'> INIT.ORA SETTING\');
DBMS_OUTPUT.put_line(\'> ****************\');
DBMS_OUTPUT.put_line(\'> Shared Pool Size = \'||spsize||\' Bytes\');
DBMS_OUTPUT.put_line(\'> DB Block Buffer = \'||blkbuf||\' Blocks\');
DBMS_OUTPUT.put_line(\'> Log Buffer = \'||logbuf||\' Bytes\');
DBMS_OUTPUT.put_line(\'> \');

if libcac < 99
then
DBMS_OUTPUT.put_line(\'*** HINT: Library Cache too low! Increase the Shared Pool Size.\');
end if;

if rowcac < 85
then
DBMS_OUTPUT.put_line(\'*** HINT: Row Cache too low! Increase the Shared Pool Size.\');
end if;

if bufcac < 90
then
DBMS_OUTPUT.put_line(\'*** HINT: Buffer Cache too low! Increase the DB Block Buffer value.\');
end if;

if redlog > 100
then
DBMS_OUTPUT.put_line(\'*** HINT: Log Buffer value is rather low!\');
end if;

end;
/

, 考虑使用dbms_space.space_usage和dbms_space包装中的其他步骤。