ORA-01157: cannot identify/lock data file导致表空间无法on
lock
朋友和我聊到一个案例,一个表空间本来有一个数据文件(已经有大量数据进入),然后他加入7个数据文件,这个时候他发现他加多了文件,想删除这些数据文件,可是又不怎么懂数据库,直接offline 表空间,然后rm掉相关数据文件,最后表空间无法online.我对其场景进行了模
朋友和我聊到一个案例,一个表空间本来有一个数据文件(已经有大量数据进入),然后他加入7个数据文件,这个时候他发现他加多了文件,想删除这些数据文件,可是又不怎么懂数据库,直接offline 表空间,然后rm掉相关数据文件,最后表空间无法online.我对其场景进行了模拟恢复测试,使用bbed和dul对其进行恢复
模拟场景
表空间有一个数据文件,里面有数据,然后加入一个新数据文件,进入offline tbs,然后rm数据文件
offline表空间后,该表空间存在的数据文件也会offline
SQL> create tablespace xifenfei datafile
2 '/u01/oracle/ora9i/oradata/xifenfei01.dbf' size 10M autoextend on next 16M;
Tablespace created.
SQL> create table chf.t_xifenfei01 tablespace xifenfei
2 as select * from dba_objects;
Table created.
SQL> create table chf.t_xifenfei02 tablespace xifenfei
2 as select * from dba_tables;
Table created.
SQL> SELECT COUNT(*) FROM CHF.T_XIFENFEI01;
COUNT(*)
----------
30758
SQL> C/01/02
1* SELECT COUNT(*) FROM CHF.T_XIFENFEI02
SQL> /
COUNT(*)
----------
865
SQL> select tablespace_name,segment_name from dba_segments
2 where segment_name like 'T_XIFENFEI%';
TABLESPACE_NAME SEGMENT_NAME
------------------------------ -------------------------
XIFENFEI T_XIFENFEI01
XIFENFEI T_XIFENFEI02
SQL> ALTER tablespace xifenfei add datafile
2 '/u01/oracle/ora9i/oradata/xifenfei02.dbf' size 16m;
Tablespace altered.
SQL> alter tablespace xifenfei offline;
Tablespace altered.
SQL> select file#,status$ from file$;
FILE# STATUS$
---------- ----------
1 2
2 2
3 2
4 2
5 2
6 2
7 2
8 2
9 2
10 2
11 2
12 2
12 rows selected.
SQL> set pages 1000
SQL> /
FILE# STATUS$
---------- ----------
1 2
2 2
3 2
4 2
5 2
6 2
7 2
8 2
9 2
10 2
11 2
12 2
12 rows selected.
SQL> select file#,status from v$datafile;
FILE# STATUS
---------- -------
1 SYSTEM
2 ONLINE
3 ONLINE
4 ONLINE
5 ONLINE
6 ONLINE
7 ONLINE
8 ONLINE
9 ONLINE
10 ONLINE
11 OFFLINE
12 OFFLINE
12 rows selected.
SQL> select file#,status from v$datafile_header;
FILE# STATUS
---------- -------
1 ONLINE
2 ONLINE
3 ONLINE
4 ONLINE
5 ONLINE
6 ONLINE
7 ONLINE
8 ONLINE
9 ONLINE
10 ONLINE
11 OFFLINE
12 OFFLINE
12 rows selected.
SQL> select tablespace_name,status from dba_tablespaces;
TABLESPACE_NAME STATUS
------------------------------ ---------
SYSTEM ONLINE
UNDOTBS1 ONLINE
TEMP ONLINE
CWMLITE ONLINE
DRSYS ONLINE
EXAMPLE ONLINE
INDX ONLINE
ODM ONLINE
TOOLS ONLINE
USERS ONLINE
XDB ONLINE
XIFENFEI OFFLINE
12 rows selected.
SQL> select ts#,name,online$ from ts$;
TS# NAME ONLINE$
---------- ------------------------------ ----------
0 SYSTEM 1
1 UNDOTBS1 1
2 TEMP 1
3 CWMLITE 1
4 DRSYS 1
5 EXAMPLE 1
6 INDX 1
7 ODM 1
8 TOOLS 1
9 USERS 1
10 XDB 1
11 UNDOTBS2 3
12 XIFENFEI 2
13 rows selected.
SQL> col name for a50
SQL> select file#,name from v$datafile;
FILE# NAME
---------- --------------------------------------------------
1 /u01/oracle/ora9i/oradata/ora9i/system01.dbf
2 /u01/oracle/ora9i/oradata/ora9i/undotbs01.dbf
3 /u01/oracle/ora9i/oradata/ora9i/cwmlite01.dbf
4 /u01/oracle/ora9i/oradata/ora9i/drsys01.dbf
5 /u01/oracle/ora9i/oradata/ora9i/example01.dbf
6 /u01/oracle/ora9i/oradata/ora9i/indx01.dbf
7 /u01/oracle/ora9i/oradata/ora9i/odm01.dbf
8 /u01/oracle/ora9i/oradata/ora9i/tools01.dbf
9 /u01/oracle/ora9i/oradata/ora9i/users01.dbf
10 /u01/oracle/ora9i/oradata/ora9i/xdb01.dbf
11 /u01/oracle/ora9i/oradata/xifenfei01.dbf
12 /u01/oracle/ora9i/oradata/xifenfei02.dbf
12 rows selected.
SQL> !rm /u01/oracle/ora9i/oradata/xifenfei02.dbf
SQL> !ls -l /u01/oracle/ora9i/oradata/xifenfei*
-rw-r----- 1 ora9i oinstall 10493952 Dec 25 20:19 /u01/oracle/ora9i/oradata/xifenfei01.dbf
SQL> alter tablespace xifenfei online;
alter tablespace xifenfei online
*
ERROR at line 1:
ORA-01157: cannot identify/lock data file 12 - see DBWR trace file
ORA-01110: data file 12: '/u01/oracle/ora9i/oradata/xifenfei02.dbf'
登入後複製
这里已经构造出来,由于由于数据文件丢失导致表空间online报ORA-01157: cannot identify/lock data file的错误
online存在数据文件
存在的数据文件online之后，表空间依然offline
SQL> alter database datafile 11 online;
Database altered.
SQL> select file#,status from v$datafile_header;
FILE# STATUS
---------- -------
1 ONLINE
2 ONLINE
3 ONLINE
4 ONLINE
5 ONLINE
6 ONLINE
7 ONLINE
8 ONLINE
9 ONLINE
10 ONLINE
11 ONLINE
12 OFFLINE
12 rows selected.
SQL> select file#,status from v$datafile;
FILE# STATUS
---------- -------
1 SYSTEM
2 ONLINE
3 ONLINE
4 ONLINE
5 ONLINE
6 ONLINE
7 ONLINE
8 ONLINE
9 ONLINE
10 ONLINE
11 ONLINE
12 OFFLINE
12 rows selected.
SQL> select tablespace_name,status from dba_tablespaces;
TABLESPACE_NAME STATUS
------------------------------ ---------
SYSTEM ONLINE
UNDOTBS1 ONLINE
TEMP ONLINE
CWMLITE ONLINE
DRSYS ONLINE
EXAMPLE ONLINE
INDX ONLINE
ODM ONLINE
TOOLS ONLINE
USERS ONLINE
XDB ONLINE
XIFENFEI OFFLINE
12 rows selected.
SQL> select ts#,name,online$ from ts$;
TS# NAME ONLINE$
---------- -------------------------------------------------- ----------
0 SYSTEM 1
1 UNDOTBS1 1
2 TEMP 1
3 CWMLITE 1
4 DRSYS 1
5 EXAMPLE 1
6 INDX 1
7 ODM 1
8 TOOLS 1
9 USERS 1
10 XDB 1
11 UNDOTBS2 3
12 XIFENFEI 2
13 rows selected.
SQL> create table chf.t_1 tablespace xifenfei
2 as select * from dual;
as select * from dual
*
ERROR at line 2:
ORA-01542: tablespace 'XIFENFEI' is offline, cannot allocate space in it
登入後複製
由于表空间无法online,因此对该表空间分配报ORA-01542错误
使用bbed构造数据文件欺骗数据库
[ora9i@xifenfei tmp]$ dd if=/dev/zero of=/u01/oracle/ora9i/oradata/xifenfei02.dbf
> bs=8192 count=2049
2049+0 records in
2049+0 records out
BBED> copy file 11 block 1 to file 12 block 1
File: /u01/oracle/ora9i/oradata/xifenfei02.dbf (12)
Block: 1 Offsets: 0 to 511 Dba:0x03000001
------------------------------------------------------------------------
0b020000 0100c002 00000000 00000104 1deb0000 00002009 00000008 329bf29e
4f524139 49000000 11010000 00050000 00200000 0b000300 00000000 00000000
BBED> set count 32
COUNT 32
BBED> m /x 0c
Warning: contents of previous BIFILE will be lost. Proceed? (Y/N) y
File: /u01/oracle/ora9i/oradata/xifenfei02.dbf (12)
Block: 1 Offsets: 280 to 311 Dba:0x03000001
------------------------------------------------------------------------
0c000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
BBED> m /x 0c
File: /u01/oracle/ora9i/oradata/xifenfei02.dbf (12)
Block: 1 Offsets: 52 to 83 Dba:0x03000001
------------------------------------------------------------------------
0c000300 00000000 00000000 00000000 00000000 00000000 00000000 00000000
BBED> sum apply
Check value for File 12, Block 1:
current = 0xad21, required = 0xad21
SQL> alter tablespace xifenfei online;
alter tablespace xifenfei online
*
ERROR at line 1:
ORA-01122: database file 12 failed verification check
ORA-01110: data file 12: '/u01/oracle/ora9i/oradata/xifenfei02.dbf'
ORA-01251: Unknown File Header Version read for file number 12
SQL> !oerr ora 01251
01251, 00000, "Unknown File Header Version read for file number %s"
// *Cause: Read of the file header returned a record but its version cannot
// be identified. Either the header has been corrupted, or the file
// is not a valid database file.
// *Action: Have the operating system make the correct file available to
// the database, or recover the file.
BBED> m /x 01000003
Warning: contents of previous BIFILE will be lost. Proceed? (Y/N) y
File: /u01/oracle/ora9i/oradata/xifenfei02.dbf (12)
Block: 1 Offsets: 4 to 36 Dba:0x03000001
------------------------------------------------------------------------
01000003 00000000 00000104 21ad0000 00002009 00000008 329bf29e 4f524139
BBED> sum apply
Check value for File 12, Block 1:
current = 0xace1, required = 0xace1
SQL> alter tablespace xifenfei online;
alter tablespace xifenfei online
*
ERROR at line 1:
ORA-01122: database file 12 failed verification check
ORA-01110: data file 12: '/u01/oracle/ora9i/oradata/xifenfei02.dbf'
ORA-01203: wrong incarnation of this file - wrong creation SCN
BBED> m /x 613B0300
Warning: contents of previous BIFILE will be lost. Proceed? (Y/N) y
File: /u01/oracle/ora9i/oradata/xifenfei02.dbf (12)
Block: 1 Offsets: 100 to 131 Dba:0x03000001
------------------------------------------------------------------------
613b0300 00000000 f35bb133 f39bae33 b46c0200 00000000 00000000 00000000
BBED> sum apply
Check value for File 12, Block 1:
current = 0xa0c9, required = 0xa0c9
--提示数据文件scn比控制文件新(由于正常数据文件online过)
SQL> alter tablespace xifenfei online;
alter tablespace xifenfei online
*
ERROR at line 1:
ORA-01122: database file 12 failed verification check
ORA-01110: data file 12: '/u01/oracle/ora9i/oradata/xifenfei02.dbf'
ORA-01207: file is more recent than controlfile - old controlfile
SQL> set lines 160
SQL> col name for a50
SQL> select ts#,file#,BYTES/1024/1024/1024 status,enabled,
2 to_char(checkpoint_change#,'999999999999999') "SCN",
3 to_char(last_change#,'999999999999999')"STOP_SCN",
4 name from v$datafile;
TS# FILE# STATUS ENABLED SCN STOP_SCN NAME
----- --- ---------- ---------- -------- ------------- ---------------------------------------------
0 1 .37109375 READ WRITE 198231 /u01/oracle/ora9i/oradata/ora9i/system01.dbf
1 2 .1953125 READ WRITE 198231 /u01/oracle/ora9i/oradata/ora9i/undotbs01.dbf
3 3 .01953125 READ WRITE 198231 /u01/oracle/ora9i/oradata/ora9i/cwmlite01.dbf
4 4 .01953125 READ WRITE 198231 /u01/oracle/ora9i/oradata/ora9i/drsys01.dbf
5 5 .145874023 READ WRITE 198231 /u01/oracle/ora9i/oradata/ora9i/example01.dbf
6 6 .024414063 READ WRITE 198231 /u01/oracle/ora9i/oradata/ora9i/indx01.dbf
7 7 .01953125 READ WRITE 198231 /u01/oracle/ora9i/oradata/ora9i/odm01.dbf
8 8 .009765625 READ WRITE 198231 /u01/oracle/ora9i/oradata/ora9i/tools01.dbf
9 9 .024414063 READ WRITE 198231 /u01/oracle/ora9i/oradata/ora9i/users01.dbf
10 10 .043945313 READ WRITE 198231 /u01/oracle/ora9i/oradata/ora9i/xdb01.dbf
12 11 .009765625 DISABLED 228353 228353 /u01/oracle/ora9i/oradata/xifenfei01.dbf
12 12 0 DISABLED 213917 213917 /u01/oracle/ora9i/oradata/xifenfei02.dbf
12 rows selected.
SQL> set pages 100
SQL> set linesize 150
SQL> select ts#,file#,TABLESPACE_NAME,status,
2 to_char(CREATION_TIME,'yyyy-mm-dd hh24:mi:ss') CREATE_TIME,
3 to_char(checkpoint_change#,'9999999999999999') "SCN",
4 to_char(RESETLOGS_CHANGE#,'9999999999999999') "RESETLOGS SCN",FUZZY
from v$datafile_header; 5
TS# FILE# TABLESPACE_NAME STATUS CREATE_TIME SCN RESETLOGS SCN FUZ
--- ----- ---------------- ------- ------------------- --------- ----------------- ---
0 1 SYSTEM ONLINE 2004-03-10 12:17:49 198231 158900 YES
1 2 UNDOTBS1 ONLINE 2004-03-10 20:30:20 198231 158900 YES
3 3 CWMLITE ONLINE 2004-03-10 12:18:10 198231 158900 YES
4 4 DRSYS ONLINE 2004-03-10 12:18:11 198231 158900 YES
5 5 EXAMPLE ONLINE 2004-03-10 12:18:12 198231 158900 YES
6 6 INDX ONLINE 2004-03-10 12:18:16 198231 158900 YES
7 7 ODM ONLINE 2004-03-10 12:18:17 198231 158900 YES
8 8 TOOLS ONLINE 2004-03-10 12:18:19 198231 158900 YES
9 9 USERS ONLINE 2004-03-10 12:18:19 198231 158900 YES
10 10 XDB ONLINE 2004-03-10 12:18:20 198231 158900 YES
12 11 XIFENFEI OFFLINE 2014-12-25 17:57:07 228353 158900 NO
0 12 OFFLINE 0 0
12 rows selected.
BBED> m /x 9D430300
File: /u01/oracle/ora9i/oradata/xifenfei02.dbf (12)
Block: 1 Offsets: 140 to 171 Dba:0x03000001
------------------------------------------------------------------------
9d430300 00000000 f670b133 01000000 02000000 fc4e0000 10000000 02000000
BBED> SUM APPLY
Check value for File 12, Block 1:
current = 0x9982, required = 0x9982
SQL> ALTER TABLESPACE XIFENFEI ONLINE;
Tablespace altered.
登入後複製
在bbed的恢复过程中出现以下常见错误:
ORA-01122: database file 12 failed verification check
ORA-01110: data file 12: ‘/u01/oracle/ora9i/oradata/xifenfei02.dbf’
ORA-01251: Unknown File Header Version read for file number 12
这个主要是块号和块地址不一匹配,导致数据库无法识别
ORA-01122: database file 12 failed verification check
ORA-01110: data file 12: ‘/u01/oracle/ora9i/oradata/xifenfei02.dbf’
ORA-01203: wrong incarnation of this file – wrong creation SCN
这个由于数据文件头的创建scn和控制文件以及file$中的记录不一致
ORA-01122: database file 12 failed verification check
ORA-01110: data file 12: ‘/u01/oracle/ora9i/oradata/xifenfei02.dbf’
ORA-01207: file is more recent than controlfile – old controlfile
这个由于正常数据文件online过,或者你构造文件头使用的scn大于需要构造文件在控制文件中记录的scn值
后续处理
SQL> SELECT COUNT(*) FROM CHF.T_XIFENFEI01;
COUNT(*)
----------
30758
SQL> C/01/02
1* SELECT COUNT(*) FROM CHF.T_XIFENFEI02
SQL> /
COUNT(*)
----------
865
SQL> ALTER DATABASE DATAFILE 12 OFFLINE DROP;
Database altered.
登入後複製
证明通过bbed,模拟数据文件,使用完美恢复数据内容
dul恢复
SQL> ALTER TABLESPACE XIFENFEI OFFLINE;
Tablespace altered.
[ora9i@xifenfei dul]$ ./dul
Data UnLoader: 10.2.0.5.33 - Internal Only - on Thu Dec 25 21:18:54 2014
with 64-bit io functions
Copyright (c) 1994 2014 Bernard van Duijnen All rights reserved.
Strictly Oracle Internal Use Only
Within one week you will need a more recent DUL version for this os
Found db_id = 2666699570
Found db_name = ORA9I
DUL> bootstrap;
Probing file = 1, block = 417
database version 9 bootstrap$ at file 1, block 377
. unloading table BOOTSTRAP$
DUL: Warning: block number is non zero but marked deferred trying to process it anyhow
57 rows unloaded
DUL: Warning: Dictionary cache DC_BOOTSTRAP is empty
Reading BOOTSTRAP.dat 57 entries loaded
Parsing Bootstrap$ contents
Generating dict.ddl for version 9
OBJ$: segobjno 18, file 1 block 121
TAB$: segobjno 2, tabno 1, file 1 block 25
COL$: segobjno 2, tabno 5, file 1 block 25
USER$: segobjno 10, tabno 1, file 1 block 89
Running generated file "@dict.ddl" to unload the dictionary tables
. unloading table OBJ$ 31490 rows unloaded
. unloading table TAB$ 909 rows unloaded
. unloading table COL$ 35582 rows unloaded
. unloading table USER$ 63 rows unloaded
Reading USER.dat 63 entries loaded
Reading OBJ.dat 31490 entries loaded and sorted 31490 entries
Reading TAB.dat 909 entries loaded
Reading COL.dat 35582 entries loaded and sorted 35582 entries
Reading BOOTSTRAP.dat 57 entries loaded
DUL: Warning: Recreating file "dict.ddl"
Generating dict.ddl for version 9
OBJ$: segobjno 18, file 1 block 121
TAB$: segobjno 2, tabno 1, file 1 block 25
COL$: segobjno 2, tabno 5, file 1 block 25
USER$: segobjno 10, tabno 1, file 1 block 89
TABPART$: segobjno 230, file 1 block 1657
INDPART$: segobjno 234, file 1 block 1689
TABCOMPART$: segobjno 249, file 1 block 1809
INDCOMPART$: segobjno 253, file 1 block 1841
TABSUBPART$: segobjno 240, file 1 block 1737
INDSUBPART$: segobjno 245, file 1 block 1777
IND$: segobjno 2, tabno 3, file 1 block 25
ICOL$: segobjno 2, tabno 4, file 1 block 25
LOB$: segobjno 2, tabno 6, file 1 block 25
COLTYPE$: segobjno 2, tabno 7, file 1 block 25
TYPE$: segobjno 296, tabno 1, file 1 block 2129
COLLECTION$: segobjno 296, tabno 2, file 1 block 2129
ATTRIBUTE$: segobjno 296, tabno 3, file 1 block 2129
LOBFRAG$: segobjno 258, file 1 block 1881
LOBCOMPPART$: segobjno 261, file 1 block 1905
UNDO$: segobjno 15, file 1 block 105
TS$: segobjno 6, tabno 2, file 1 block 57
PROPS$: segobjno 101, file 1 block 769
Running generated file "@dict.ddl" to unload the dictionary tables
. unloading table OBJ$
DUL: Warning: Recreating file "OBJ.ctl"
31490 rows unloaded
. unloading table TAB$
DUL: Warning: Recreating file "TAB.ctl"
909 rows unloaded
. unloading table COL$
DUL: Warning: Recreating file "COL.ctl"
35582 rows unloaded
. unloading table USER$
DUL: Warning: Recreating file "USER.ctl"
63 rows unloaded
. unloading table TABPART$ 55 rows unloaded
. unloading table INDPART$ 128 rows unloaded
. unloading table TABCOMPART$ 0 rows unloaded
. unloading table INDCOMPART$ 0 rows unloaded
. unloading table TABSUBPART$ 0 rows unloaded
. unloading table INDSUBPART$ 0 rows unloaded
. unloading table IND$ 1396 rows unloaded
. unloading table ICOL$ 1842 rows unloaded
. unloading table LOB$ 427 rows unloaded
. unloading table COLTYPE$ 1160 rows unloaded
. unloading table TYPE$ 956 rows unloaded
. unloading table COLLECTION$ 250 rows unloaded
. unloading table ATTRIBUTE$ 3623 rows unloaded
. unloading table LOBFRAG$ 0 rows unloaded
. unloading table LOBCOMPPART$ 0 rows unloaded
. unloading table UNDO$ 21 rows unloaded
. unloading table TS$ 13 rows unloaded
. unloading table PROPS$ 25 rows unloaded
Reading USER.dat 63 entries loaded
Reading OBJ.dat 31490 entries loaded and sorted 31490 entries
Reading TAB.dat 909 entries loaded
Reading COL.dat 35582 entries loaded and sorted 35582 entries
Reading TABPART.dat 55 entries loaded and sorted 55 entries
Reading TABCOMPART.dat 0 entries loaded and sorted 0 entries
Reading TABSUBPART.dat 0 entries loaded and sorted 0 entries
Reading INDPART.dat 128 entries loaded and sorted 128 entries
Reading INDCOMPART.dat 0 entries loaded and sorted 0 entries
Reading INDSUBPART.dat 0 entries loaded and sorted 0 entries
Reading IND.dat 1396 entries loaded
Reading LOB.dat 427 entries loaded
Reading ICOL.dat 1842 entries loaded
Reading COLTYPE.dat 1160 entries loaded
Reading TYPE.dat 956 entries loaded
Reading ATTRIBUTE.dat 3623 entries loaded
Reading COLLECTION.dat 250 entries loaded
Reading BOOTSTRAP.dat 57 entries loaded
Reading LOBFRAG.dat 0 entries loaded and sorted 0 entries
Reading LOBCOMPPART.dat 0 entries loaded and sorted 0 entries
Reading UNDO.dat 21 entries loaded
Reading TS.dat 13 entries loaded
Reading PROPS.dat 25 entries loaded
Database character set is ZHS16GBK
Database national character set is AL16UTF16
DUL> unload table chf.t_xifenfei01;
. unloading table T_XIFENFEI01 30758 rows unloaded
DUL> unload table chf.t_xifenfei02;
. unloading table T_XIFENFEI02 865 rows unloaded
DUL>
登入後複製
这里证明,在表空间不能online的情况下,dul处理类似故障很轻松(但是需要重建表空间,bbed处理的从原理上可以不重建表空间),当然如果涉及的对象很多,而丢失的文件很少,可能bbed也不失为一种很不错的选择.
另外补充:如果表空间丢失的文件包含数据,也可以通过类似bbed和dul方法处理:bbed 让表空间online之后需要考虑跳过丢失文件;dul处理完全相同
- 使用 dul 挖数据文件初试
- dul 10支持oracle 11g r2
- DUL10直接支持ORACLE 8.0
- 密码保护：dul扫描磁盘抢救数据
- 密码保护：使用dul恢复asm中数据
- dul支持ORACLE 12C CDB数据库恢复
- asm disk header 彻底损坏恢复
- dul恢复truncate表测试
原文地址：ORA-01157: cannot identify/lock data file导致表空间无法on, 感谢原作者分享。
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Jdk1.5以後，在java.util.concurrent.locks套件下，有一組實現線程同步的介面和類，說到線程的同步，可能大家都會想到synchronized關鍵字，這是java內建的關鍵字，用來處理線程同步的，但這個關鍵字有很多的缺陷，使用起來也不是很方便和直觀，所以就出現了Lock，下面，我們就來對比著講解Lock。通常我們在使用synchronized關鍵字的時候會遇到下面這些問題：（1）不可控性，無法做到隨心所欲的加鎖和釋放鎖。 （2）效率比較低下，例如我們現在並發的讀兩個文件，讀與讀之
Java中Lock的使用方式有哪些？
Apr 23, 2023 pm 08:52 PM
1.作用（1）Lock方式來獲取鎖支援中斷、超時不獲取、是非阻塞的（2）提高了語義化，哪裡加鎖，哪裡解鎖都得寫出來（3）Lock顯式鎖可以給我們帶來很好的靈活性，但同時我們必須手動釋放鎖定（4）支援Condition條件物件（5）允許多個讀取線程同時存取共享資源2.lock用法//獲取鎖定voidlock()//如果當前線程未中斷，則取得鎖定voidlockInterruptibly()//傳回綁定至此Lock實例的新Condition實例ConditionnewCondition()//僅在呼叫時鎖定
Java Lock類別提供哪些功能？
Apr 21, 2023 am 08:16 AM
說明1、Lock是java.util.concurent套件下的接口，定義了一系列的鎖定操作方法。 2.Lock介面主要包括ReentrantLock、ReentrantReadWriteLock、ReentrantReadWriteLock、WriteLock實作類別。與Synchronized不同，Lock提供了取得鎖定、釋放鎖定等相關介面，使其使用更加靈活，操作更加複雜。實例ReentrantReadWriteLocklock=newReentrantReadWriteLock();Lockread
Java中為什麼需要提供Lock，而不只使用synchronized關鍵字？
Apr 20, 2023 pm 05:01 PM
摘要：在Java中提供了synchronized關鍵字來保證只有一個執行緒能夠存取同步程式碼區塊。既然已經提供了synchronized關鍵字，為何在Java的SDK包中，還會提供Lock介面呢？這是不是重複造輪子，多此一舉呢？今天，我們就一起來探討下這個問題。在Java中提供了synchronized關鍵字來保證只有一個執行緒能夠存取同步程式碼區塊。既然已經提供了synchronized關鍵字，為何在Java的SDK包中，還會提供Lock介面呢？這是不是重複造輪子，多此一舉呢？今天，我們就一起來探討下
Java技術堆疊中的常見問題及其解決方法
Sep 06, 2023 am 09:59 AM
Java技術堆疊中的常見問題及其解決方法在開發Java應用程式時，我們常常會遇到一些問題，例如效能問題、記憶體洩漏、執行緒安全性等等。本文將介紹一些常見問題及其解決方法，並給出相應的程式碼範例。一、效能問題1.1頻繁創建物件導致的效能問題頻繁創建物件會導致垃圾回收的頻繁觸發，進而影響程式的效能。解決方法是使用物件池或快取重用物件。範例程式碼：//使用物件池重複使用對象
java中lock取得鎖定的方法有哪些
May 19, 2023 pm 01:13 PM
1.取得方法lock()、tryLock()、tryLock(longtime,TimeUnitunit)和lockInterruptibly()都是用來取得鎖的。 （1）lock()方法是平常使用得最多的一個方法，就是用來取得鎖。如果鎖已被其他線程獲取，則進行等待。 （2）tryLock()方法是有回傳值的，它表示用來嘗試取得鎖，如果取得成功，則傳回true，如果取得失敗（即鎖已被其他執行緒取得），則傳回false，也就說這個方法無論如何都會立即返回。在拿不到鎖時不會一直在那裡等待。 （3）tryLoc
Java中Lock和Synchronized的差別是什麼
Apr 17, 2023 pm 07:19 PM
1.從功能角度來看Lock和Synchronized都是java中去用來解決線程安全問題的一個工具2.從特性來看Synchronized是java中的同步關鍵字，Lock是J.U.C包中提供的接口，而這個介面有很多的實現類，包括ReentrantLock這樣重入鎖的實現，Synchronized可以透過兩種方式去控制鎖的力度一種把synchronized關鍵字修飾在方法層面，另一種是修飾在程式碼區塊上，可以透過synchronized加鎖物件的生命週期，來控制鎖的作用範圍，鎖定物件是靜態物件或類別對
透過 Auth0 Lock 實現 PHP 安全驗證
Jul 24, 2023 am 11:16 AM
透過Auth0Lock實現PHP安全驗證隨著網際網路的發展，越來越多的應用程式需要進行使用者身份驗證和安全驗證，以保護使用者隱私和資料安全。 PHP是一種廣泛使用的後端語言，提供了許多方法來實現安全驗證。而Auth0是一個流行的身份驗證和授權平台，為開發人員提供了一個靈活和安全的方式來實現使用者身份驗證。 Auth0Lock是Auth0提供的一個
