前言
本文对于lob字段删除插入的重用规则进行测试。
PCTVERSION指定用于维护LOB的旧版本占总体LOB存储空间的最大百分比。默认值为10，这意味着在使用了整个LOB存储空间的10%之前，不会覆盖旧版本的LOB数据。
该参数不建议设置过大，因为会额外占用空间。
RETENTION参数已经是默认配置，推荐配置，其受UNDO_RETENTION参数的影响，并且Securefiles lob只支持RETENTION。
关于lob更详细的解释参考文章：Oracle LOB——基本概念
确认PCTVERSION参数作用
初始化环境
创建包含BLOB字段表，PCTVERSION为10，初始化区1M，每次扩展1M
conn dhw/dhw CREATE TABLESPACE TTS_NAME DATAFILE '/u01/app/oracle/oradata/utf8db/DB01.dbf' SIZE 60M REUSE AUTOEXTEND OFF; CREATE TABLE "DHW"."BLOB_TEST" ( "ID" NUMBER, "DATA" BLOB ) SEGMENT CREATION IMMEDIATE TABLESPACE "TTS_NAME" LOB ("DATA") STORE AS lob_test_col ( TABLESPACE "TTS_NAME" DISABLE STORAGE IN ROW CHUNK 8192 PCTVERSION 10 STORAGE(INITIAL 1048576 NEXT 1048576 )) Create or replace directory TEST as '/tmp'; [oracle@linux8 tmp]$ dd if=/dev/zero of=/tmp/test1m.dat bs=1M count=1 1+0 records in 1+0 records out 1048576 bytes (1.0 MB, 1.0 MiB) copied, 0.000447859 s, 2.3 GB/s [oracle@linux8 tmp]$ ls -l test1m.dat -rw-r--r-- 1 oracle oinstall 1048576 Jan 9 15:30 test1m.dat [oracle@linux8 tmp]$ SQL> select TABLE_NAME,COLUMN_NAME,PCTVERSION,RETENTION,SECUREFILE,RETENTION_TYPE,RETENTION_VALUE from dba_lobs where table_name='BLOB_TEST'; TABLE_NAME COLUMN_NAME PCTVERSION RETENTION SEC RETENTI RETENTION_VALUE ------------------------------ ------------------------------ ---------- ---------- --- ------- --------------- BLOB_TEST DATA 10 NO NO SQL> select * from dba_extents where tablespace_name='TTS_NAME'; OWNER SEGMENT_NAME PARTITION_ SEGMENT_TYPE TABLESPACE EXTENT_ID FILE_ID BLOCK_ID BYTES BLOCKS RELATIVE_FNO ------ ------------------------------ ---------- ------------------ ---------- ---------- ---------- ---------- ---------- ---------- ------------ DHW LOB_TEST_COL LOBSEGMENT TTS_NAME 0 5 256 1048576 128 5 DHW SYS_IL0000088014C00002$$ LOBINDEX TTS_NAME 0 5 136 65536 8 5 DHW BLOB_TEST TABLE TTS_NAME 0 5 128 65536 8 5复制
插入10行数据
插入10行（每行1m）数据后，lob字段数据占用10个1m的extent，extent 0为段头
DECLARE src_file BFILE := bfilename('TEST', 'test1m.dat'); dst_file BLOB; lgh_file BINARY_INTEGER; cur_id NUMBER(10); BEGIN FOR i IN 1 .. 10 ----->>> Insert 1 to 10 LOOP INSERT INTO blob_test (id, data) VALUES (lob_test_seq.nextval, empty_blob()) RETURNING id into cur_id; -- lock record SELECT data INTO dst_file FROM blob_test WHERE id = cur_id FOR UPDATE; dbms_lob.fileopen(src_file, dbms_lob.file_readonly); lgh_file := dbms_lob.getlength(src_file); dbms_lob.loadfromfile(dst_file, src_file, lgh_file); dbms_lob.fileclose(src_file); END LOOP; END; / OWNER SEGMENT_NAME PARTITION_ SEGMENT_TYPE TABLESPACE EXTENT_ID FILE_ID BLOCK_ID BYTES BLOCKS RELATIVE_FNO ------ ------------------------------ ---------- ------------------ ---------- ---------- ---------- ---------- ---------- ---------- ------------ DHW LOB_TEST_COL LOBSEGMENT TTS_NAME 0 5 256 1048576 128 5 DHW LOB_TEST_COL LOBSEGMENT TTS_NAME 1 5 384 1048576 128 5 DHW LOB_TEST_COL LOBSEGMENT TTS_NAME 2 5 512 1048576 128 5 DHW LOB_TEST_COL LOBSEGMENT TTS_NAME 3 5 640 1048576 128 5 DHW LOB_TEST_COL LOBSEGMENT TTS_NAME 4 5 768 1048576 128 5 DHW LOB_TEST_COL LOBSEGMENT TTS_NAME 5 5 896 1048576 128 5 DHW LOB_TEST_COL LOBSEGMENT TTS_NAME 6 5 1024 1048576 128 5 DHW LOB_TEST_COL LOBSEGMENT TTS_NAME 7 5 1152 1048576 128 5 DHW LOB_TEST_COL LOBSEGMENT TTS_NAME 8 5 1280 1048576 128 5 DHW LOB_TEST_COL LOBSEGMENT TTS_NAME 9 5 1408 1048576 128 5 DHW LOB_TEST_COL LOBSEGMENT TTS_NAME 10 5 1536 1048576 128 5 DHW SYS_IL0000088014C00002$$ LOBINDEX TTS_NAME 0 5 136 65536 8 5 DHW BLOB_TEST TABLE TTS_NAME 0 5 128 65536 8 5 13 rows selected. select df.tablespace_name "Tablespace", totalusedspace "Used MB", (df.totalspace - tu.totalusedspace) "Free MB", df.totalspace "Total MB", round(100 * ((df.totalspace - tu.totalusedspace) / df.totalspace)) "Pct. Free" from (select tablespace_name, round(sum(bytes) / 1048576) TotalSpace from dba_data_files group by tablespace_name) df, (select round(sum(bytes) / (1024 * 1024)) totalusedspace, tablespace_name from dba_segments group by tablespace_name) tu where df.tablespace_name = tu.tablespace_name and tu.tablespace_name='TTS_NAME'; Tablespace Used MB Free MB Total MB Pct. Free ---------------------- ----------- ----------- ----------- ---------- TTS_NAME 11 49 60 82 SQL> select * from BLOB_TEST; ID DATA ---------- ------------------------------------------------------------------------------------------------------------------------ 524 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 525 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 526 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 527 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 528 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 529 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 530 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 531 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 532 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 533 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 10 rows selected.复制
删除数据后再次插入
15:58:29 SQL> delete from BLOB_TEST; 10 rows deleted. 15:59:29 SQL> commit ; Commit complete.复制
先插入9行，空间占用不变
DECLARE src_file BFILE := bfilename('TEST', 'test1m.dat'); dst_file BLOB; lgh_file BINARY_INTEGER; cur_id NUMBER(10); BEGIN FOR i IN 1 .. 9 ----->>> Insert 1 to 9 LOOP INSERT INTO blob_test (id, data) VALUES (lob_test_seq.nextval, empty_blob()) RETURNING id into cur_id; -- lock record SELECT data INTO dst_file FROM blob_test WHERE id = cur_id FOR UPDATE; dbms_lob.fileopen(src_file, dbms_lob.file_readonly); lgh_file := dbms_lob.getlength(src_file); dbms_lob.loadfromfile(dst_file, src_file, lgh_file); dbms_lob.fileclose(src_file); END LOOP; END; / Tablespace Used MB Free MB Total MB Pct. Free ---------------------- ----------- ----------- ----------- ---------- TTS_NAME 11 49 60 82复制
再次插入1行，新分配了一个extent，因为PCTVERSION为10，最后1行（10%）的数据旧版本被保留。
DECLARE src_file BFILE := bfilename('TEST', 'test1m.dat'); dst_file BLOB; lgh_file BINARY_INTEGER; cur_id NUMBER(10); BEGIN FOR i IN 1 .. 1 ----->>> Insert 1 to 1 LOOP INSERT INTO blob_test (id, data) VALUES (lob_test_seq.nextval, empty_blob()) RETURNING id into cur_id; -- lock record SELECT data INTO dst_file FROM blob_test WHERE id = cur_id FOR UPDATE; dbms_lob.fileopen(src_file, dbms_lob.file_readonly); lgh_file := dbms_lob.getlength(src_file); dbms_lob.loadfromfile(dst_file, src_file, lgh_file); dbms_lob.fileclose(src_file); END LOOP; END; / Tablespace Used MB Free MB Total MB Pct. Free ---------------------- ----------- ----------- ----------- ---------- TTS_NAME 12 48 60 80 OWNER SEGMENT_NAME PARTITION_ SEGMENT_TYPE TABLESPACE EXTENT_ID FILE_ID BLOCK_ID BYTES BLOCKS RELATIVE_FNO ------ ------------------------------ ---------- ------------------ ---------- ---------- ---------- ---------- ---------- ---------- ------------ DHW LOB_TEST_COL LOBSEGMENT TTS_NAME 0 5 256 1048576 128 5 DHW LOB_TEST_COL LOBSEGMENT TTS_NAME 1 5 384 1048576 128 5 DHW LOB_TEST_COL LOBSEGMENT TTS_NAME 2 5 512 1048576 128 5 DHW LOB_TEST_COL LOBSEGMENT TTS_NAME 3 5 640 1048576 128 5 DHW LOB_TEST_COL LOBSEGMENT TTS_NAME 4 5 768 1048576 128 5 DHW LOB_TEST_COL LOBSEGMENT TTS_NAME 5 5 896 1048576 128 5 DHW LOB_TEST_COL LOBSEGMENT TTS_NAME 6 5 1024 1048576 128 5 DHW LOB_TEST_COL LOBSEGMENT TTS_NAME 7 5 1152 1048576 128 5 DHW LOB_TEST_COL LOBSEGMENT TTS_NAME 8 5 1280 1048576 128 5 DHW LOB_TEST_COL LOBSEGMENT TTS_NAME 9 5 1408 1048576 128 5 DHW LOB_TEST_COL LOBSEGMENT TTS_NAME 10 5 1536 1048576 128 5 DHW LOB_TEST_COL LOBSEGMENT TTS_NAME 11 5 1664 1048576 128 5 DHW SYS_IL0000088014C00002$$ LOBINDEX TTS_NAME 0 5 136 65536 8 5 DHW BLOB_TEST TABLE TTS_NAME 0 5 128 65536 8 5 14 rows selected.复制
确认覆盖的数据
覆盖的数据是前9行，闪回查询报ORA-01555，第10行数据闪回查询正常
16:06:12 SQL> select * from BLOB_TEST as of timestamp to_timestamp('2023-01-09 15:58:27','yyyy-mm-dd hh24:mi:ss') ; ERROR: ORA-01555: snapshot too old: rollback segment number with name "" too small ORA-22924: snapshot too old 16:06:19 SQL> select * from BLOB_TEST as of timestamp to_timestamp('2023-01-09 15:58:27','yyyy-mm-dd hh24:mi:ss') where id=533; ID DATA ---------- ------------------------------------------------------------------------------------------------------------------------ 533 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 16:07:04 SQL> select * from BLOB_TEST as of timestamp to_timestamp('2023-01-09 15:58:27','yyyy-mm-dd hh24:mi:ss') where id=532; ERROR: ORA-01555: snapshot too old: rollback segment number with name "" too small ORA-22924: snapshot too old 16:07:13 SQL> select * from BLOB_TEST as of timestamp to_timestamp('2023-01-09 15:58:27','yyyy-mm-dd hh24:mi:ss') where id=524; ERROR: ORA-01555: snapshot too old: rollback segment number with name "" too small ORA-22924: snapshot too old复制
确认RETENTION参数作用
初始化环境，修改lob为RETENTION
SQL> alter table BLOB_TEST modify lob (DATA) (retention ); Table altered. SQL> truncate table BLOB_TEST; Table truncated. SQL> alter database datafile '/u01/app/oracle/oradata/utf8db/DB01.dbf' resize 15m; SQL> select TABLE_NAME,COLUMN_NAME,PCTVERSION,RETENTION,SECUREFILE,RETENTION_TYPE,RETENTION_VALUE from dba_lobs where table_name='BLOB_TEST'; TABLE_NAME COLUMN_NAME PCTVERSION RETENTION SEC RETENTI RETENTION_VALUE ------------------------------ ------------------------------ ---------- ---------- --- ------- --------------- BLOB_TEST DATA 900 NO YES SQL> show parameter undo NAME TYPE VALUE ------------------------------------ ----------- ------------------------------ undo_management string AUTO undo_retention integer 900 undo_tablespace string UNDOTBS1复制
插入10行数据
DECLARE src_file BFILE := bfilename('TEST', 'test1m.dat'); dst_file BLOB; lgh_file BINARY_INTEGER; cur_id NUMBER(10); BEGIN FOR i IN 1 .. 10 ----->>> Insert 1 to 10 LOOP INSERT INTO blob_test (id, data) VALUES (lob_test_seq.nextval, empty_blob()) RETURNING id into cur_id; -- lock record SELECT data INTO dst_file FROM blob_test WHERE id = cur_id FOR UPDATE; dbms_lob.fileopen(src_file, dbms_lob.file_readonly); lgh_file := dbms_lob.getlength(src_file); dbms_lob.loadfromfile(dst_file, src_file, lgh_file); dbms_lob.fileclose(src_file); END LOOP; END; / Tablespace Used MB Free MB Total MB Pct. Free ---------------------- ----------- ----------- ----------- ---------- TTS_NAME 11 4 15 27 17:08:19 SQL> select * from blob_test; ID DATA ---------- ------------------------------------------------------------------------------------------------------------------------ 608 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 609 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 610 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 611 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 612 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 613 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 614 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 615 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 616 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 617 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 10 rows selected复制
删除数据后再次插入
17:09:27 SQL> delete from blob_test; 10 rows deleted. 17:09:27 SQL> commit ;复制
在表空间数据文件自动扩展没开启的情况下，表空间剩余空间不足时，插入会覆盖
DECLARE src_file BFILE := bfilename('TEST', 'test1m.dat'); dst_file BLOB; lgh_file BINARY_INTEGER; cur_id NUMBER(10); BEGIN FOR i IN 1 .. 10 ----->>> Insert 1 to 10 LOOP INSERT INTO blob_test (id, data) VALUES (lob_test_seq.nextval, empty_blob()) RETURNING id into cur_id; -- lock record SELECT data INTO dst_file FROM blob_test WHERE id = cur_id FOR UPDATE; dbms_lob.fileopen(src_file, dbms_lob.file_readonly); lgh_file := dbms_lob.getlength(src_file); dbms_lob.loadfromfile(dst_file, src_file, lgh_file); dbms_lob.fileclose(src_file); END LOOP; END; / Tablespace Used MB Free MB Total MB Pct. Free ---------------------- ----------- ----------- ----------- ---------- TTS_NAME 13 2 15 13复制
在表空间数据文件自动扩展开启情况下，会自动扩容表空间，旧版本数据保留根据undo_retention配置
17:16:25 SQL> alter database datafile '/u01/app/oracle/oradata/utf8db/DB01.dbf' autoextend on ; Database altered. 17:16:32 SQL> select * from blob_test; ID DATA ---------- ------------------------------------------------------------------------------------------------------------------------ 618 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 619 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 620 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 621 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 622 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 623 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 624 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 625 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 626 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 627 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 10 rows selected. 17:16:56 SQL> delete from blob_test; 10 rows deleted. 17:17:02 SQL> commit ; Commit complete. 17:17:03 SQL>复制
插入数据，旧版本数据都在
DECLARE src_file BFILE := bfilename('TEST', 'test1m.dat'); dst_file BLOB; lgh_file BINARY_INTEGER; cur_id NUMBER(10); BEGIN FOR i IN 1 .. 10 ----->>> Insert 1 to 10 LOOP INSERT INTO blob_test (id, data) VALUES (lob_test_seq.nextval, empty_blob()) RETURNING id into cur_id; -- lock record SELECT data INTO dst_file FROM blob_test WHERE id = cur_id FOR UPDATE dbms_lob.fileopen(src_file, dbms_lob.file_readonly); lgh_file := dbms_lob.getlength(src_file); dbms_lob.loadfromfile(dst_file, src_file, lgh_file); dbms_lob.fileclose(src_file); END LOOP; END; / Tablespace Used MB Free MB Total MB Pct. Free ---------------------- ----------- ----------- ----------- ---------- TTS_NAME 23 2 25 8复制
闪回查询可以查到删除前全部数据
17:17:47 SQL> select * from BLOB_TEST as of timestamp to_timestamp('2023-01-09 17:16:32','yyyy-mm-dd hh24:mi:ss') ; ID DATA ---------- ------------------------------------------------------------------------------------------------------------------------ 618 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 619 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 620 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 621 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 622 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 623 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 624 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 625 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 626 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 627 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 10 rows selected. 17:19:59 SQL> select * from BLOB_TEST; ID DATA ---------- ------------------------------------------------------------------------------------------------------------------------ 628 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 629 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 630 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 631 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 632 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 633 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 634 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 635 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 636 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 637 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 10 rows selected.复制
修改undo保留期，测试释放lob旧版本，修改参数后 ，dba_lobs视图没有变化，但是已经生效，旧版本undo被覆盖，数据占用没有增长（生产环境谨慎修改undo_retention）
17:21:06 SQL> alter system set undo_retention=30; System altered. 17:21:33 SQL> select TABLE_NAME,COLUMN_NAME,PCTVERSION,RETENTION,SECUREFILE,RETENTION_TYPE,RETENTION_VALUE from dba_lobs where table_name='BLOB_TEST'; TABLE_NAME COLUMN_NAME PCTVERSION RETENTION SEC RETENTI RETENTION_VALUE ------------------------------ ------------------------------ ---------- ---------- --- ------- --------------- BLOB_TEST DATA 900 NO YES 17:22:17 SQL> delete from BLOB_TEST; 10 rows deleted. 17:22:29 SQL> commit ; Commit complete. DECLARE src_file BFILE := bfilename('TEST', 'test1m.dat'); dst_file BLOB; lgh_file BINARY_INTEGER; cur_id NUMBER(10); BEGIN FOR i IN 1 .. 10 ----->>> Insert 1 to 10 LOOP INSERT INTO blob_test (id, data) VALUES (lob_test_seq.nextval, empty_blob()) RETURNING id into cur_id; -- lock record SELECT data INTO dst_file FROM blob_test WHERE id = cur_id FOR UPDATE; dbms_lob.fileopen(src_file, dbms_lob.file_readonly); lgh_file := dbms_lob.getlength(src_file); dbms_lob.loadfromfile(dst_file, src_file, lgh_file); dbms_lob.fileclose(src_file); END LOOP; END; / Tablespace Used MB Free MB Total MB Pct. Free ---------------------- ----------- ----------- ----------- ---------- TTS_NAME 23 2 25 8复制
最后修改时间：2023-01-12 09:42:59
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