从逻辑上看，这段代码可以用以下代码进行模拟，
declare
aaa clob;
begin
aaa := empty_clob();
aaa := 'aaaaaaaaaaaaaaaaaaaabaaaaaaaaaaaaaaaaaaaaabaaaaaaaaaaaaaaaaaaaaaabaaaaaaaaabaaaaaaaaaaaaaaaaaaaaaaabaaaaaaaaaaaaabaaaaaaaaaaaaa';
for i in 1..10000 loop
aaa := replace(aaa, 'b', ';;');
end loop;
end;
aaa clob;
begin
aaa := empty_clob();
aaa := 'aaaaaaaaaaaaaaaaaaaabaaaaaaaaaaaaaaaaaaaaabaaaaaaaaaaaaaaaaaaaaaabaaaaaaaaabaaaaaaaaaaaaaaaaaaaaaaabaaaaaaaaaaaaabaaaaaaaaaaaaa';
for i in 1..10000 loop
aaa := replace(aaa, 'b', ';;');
end loop;
end;
我们知道，在PLSQL中的LOB类型变量是占用临时表空间的。但是，从以上代码看，CLOB变量aaa的初始值并没有占用太大空间。我们在测试环境上运行该语句，用以下语句观察其临时表空间占用情况。
SELECT b.tablespace,
ROUND(((b.blocks*p.value)/1024/1024),2)||'M' "SIZE",
b.CONTENTS,
s.sql_text,
a.sid||','||a.serial# SID_SERIAL,
a.username,
a.program,
sysdate as log_date
FROM sys.v_$session a,
sys.v_$sort_usage b,
sys.v_$parameter p,
v$sqlarea s
WHERE p.name = 'db_block_size'
AND a.saddr = b.session_addr
AND a.sql_address = s.address and a.sql_hash_value = s.hash_value
ORDER BY b.tablespace, b.blocks;
TABLESPACE SIZE CONTENTS SQL_TEXT SID_SERIAL USERNAME PROGRAM LOG_DATE
---------------------------------------------------------------------------------
TEMP 37M TEMPORARY declare aaa clob; begin aaa := empty_clob(); aaa := 'aaaaaaaaaaaaaaaaaaaabaaaaaaaaaaaaaaaaaaaaabaaaaaaaaaaaaaaaaaaaaaabaaaaaaaaabaaaaaaaaaaaaaaaaaaaaaaabaaaaaaaaaaaaabaaaaaaaaaaaaa'; for i in 1..1000000000 loop aaa := replace(aaa, 'a', ';;'); end loop; end; 137,28675 DEMO plsqldev.exe 8/15/2007 11:42:11
ROUND(((b.blocks*p.value)/1024/1024),2)||'M' "SIZE",
b.CONTENTS,
s.sql_text,
a.sid||','||a.serial# SID_SERIAL,
a.username,
a.program,
sysdate as log_date
FROM sys.v_$session a,
sys.v_$sort_usage b,
sys.v_$parameter p,
v$sqlarea s
WHERE p.name = 'db_block_size'
AND a.saddr = b.session_addr
AND a.sql_address = s.address and a.sql_hash_value = s.hash_value
ORDER BY b.tablespace, b.blocks;
TABLESPACE SIZE CONTENTS SQL_TEXT SID_SERIAL USERNAME PROGRAM LOG_DATE
---------------------------------------------------------------------------------
TEMP 37M TEMPORARY declare aaa clob; begin aaa := empty_clob(); aaa := 'aaaaaaaaaaaaaaaaaaaabaaaaaaaaaaaaaaaaaaaaabaaaaaaaaaaaaaaaaaaaaaabaaaaaaaaabaaaaaaaaaaaaaaaaaaaaaaabaaaaaaaaaaaaabaaaaaaaaaaaaa'; for i in 1..1000000000 loop aaa := replace(aaa, 'a', ';;'); end loop; end; 137,28675 DEMO plsqldev.exe 8/15/2007 11:42:11
