PostgreSQL PG 数据文件灾难恢复 – 解析与数据pg_filedump

作者

digoal

日期

2017-03-10

标签

PostgreSQL , 数据文件 , pg_filedump , 安全 , TDE


背景

俗话说常在河边站哪有不湿鞋,作为一名战斗在一线的DBA或者开发者,可能有遇到过磁盘损坏,磁盘阵列损坏,如果有备份或者备库的话,还好。

如果没有备份,或者没有备库(通常有一些小型或者创业型的企业),那么遇到磁盘损坏或者其他原因(比如掉电文件系统损坏),导致数据库的数据文件并不完整时,如何从有限的资料中找出数据呢?

比如PostgreSQL,如果读到坏块,会报块不可读的错误,这种情况下通过设置zero_damaged_pages=on可以跳过损坏的数据块。

如果连元数据都损坏了,又或者坏了一些磁盘,只有某些表空间被幸免于难,这些情况下你的数据库都已经无法启动时,如何能从有限的数据文件中找回数据呢?

 

 

数据文件解析pg_filedump

 

 

pg_filedump是PostgreSQL社区托管的一个项目,类似于pg_xlogdump,不需要开启数据库,可以直接从数据文件中将数据dump出来。

pg_filedump实际上可以DUMP 堆表、索引数据文件,控制文件的内容。(从pg_filedump引用的头文件也能看出端倪)

安装很简单

 

 

git clone git://git.postgresql.org/git/pg_filedump.git  
  
cd pg_filedump  
  
export PATH=/home/digoal/pgsql9.6/bin:$PATH  
  
make ; make install  

命令帮助如下,通常来说,你只需要指定需要DUMP的文件即可。

如果文件的块头损坏了,那么你可以手工指定一些信息,包括块大小,段大小,解析哪个块,根据什么格式解析(字段类型列表)等。

 

 

pg_filedump [-abcdfhikxy] [-R startblock [endblock]] [-D attrlist] [-S blocksize] [-s segsize] [-n segnumber] file  
  
Defaults are: relative addressing, range of the entire file, block size  
              as listed on block 0 in the file  
  
The following options are valid for heap and index files:  
  -a  Display absolute addresses when formatting (Block header  
      information is always block relative)  
  -b  Display binary block images within a range (Option will turn  
      off all formatting options)  
  -d  Display formatted block content dump (Option will turn off  
      all other formatting options)  
  -D  Try to decode tuples using given comma separated list of types.  
      List of supported types:  
        * bigint  
        * bigserial  
        * bool  
        * char  
        * charN     -- char(n)  
        * date  
        * float  
        * float4  
        * float8  
        * int  
        * json  
        * macaddr  
        * name  
        * oid  
        * real  
        * serial  
        * smallint  
        * smallserial  
        * text  
        * time  
        * timestamp  
        * timetz  
        * uuid  
        * varchar  
        * varcharN -- varchar(n)  
        * xid  
        * xml  
        * ~        -- ignores are attributes left in a tuple  
  -f  Display formatted block content dump along with interpretation  
  -h  Display this information  
  -i  Display interpreted item details  
  -k  Verify block checksums  
  -R  Display specific block ranges within the file (Blocks are  
      indexed from 0)  
        [startblock]: block to start at  
        [endblock]: block to end at  
      A startblock without an endblock will format the single block  
  -s  Force segment size to [segsize]  
  -n  Force segment number to [segnumber]  
  -S  Force block size to [blocksize]  
  -x  Force interpreted formatting of block items as index items  
  -y  Force interpreted formatting of block items as heap items  
  
The following options are valid for control files:  
  -c  Interpret the file listed as a control file  
  -f  Display formatted content dump along with interpretation  
  -S  Force block size to [blocksize]  
  
In most cases it's recommended to use the -i and -f options to get  
the most useful dump output.  

pg_filedump使用举例

 

 

1. 创建测试表

postgres=# create table digoal(id int, info text, crt_time timestamp);  
CREATE TABLE  

2. 插入测试数据

postgres=# insert into digoal select generate_series(1,1000000),md5(random()::text), clock_timestamp();  
INSERT 0 1000000  

3. 找出表对应的数据文件

postgres=# select pg_relation_filepath('digoal');  
 pg_relation_filepath   
----------------------  
 base/13269/173369  
(1 row)  

4. 调用checkpoint,把数据刷盘,便于我们接下来的观察

checkpoint;  

5. 使用pg_filedump直接读取数据文件,导出数据

-> cd $PGDATA/base/13269  
-> pg_filedump -i -f ./173369  
  
输出截取  
*******************************************************************  
* PostgreSQL File/Block Formatted Dump Utility - Version 9.6.0  
*  
* File: ./173369  
* Options used: -i -f   
*  
* Dump created on: Sun Mar 12 00:28:56 2017  
*******************************************************************  
  
首先是块的头部内容

Block    0 ********************************************************  
<Header> -----  
 Block Offset: 0x00000000         Offsets: Lower     452 (0x01c4)  
 Block: Size 8192  Version    4            Upper     488 (0x01e8)  
 LSN:  logid     61 recoff 0xe69d6490      Special  8192 (0x2000)  
 Items:  107                      Free Space:   36  
 Checksum: 0x0000  Prune XID: 0x00000000  Flags: 0x0000 ()  
 Length (including item array): 452  

...
 
然后是DATA部分,
<Data> ------ 
 Item   1 -- Length:   72  Offset: 8120 (0x1fb8)  Flags: NORMAL
  XMIN: 88072212  XMAX: 88072214  CID|XVAC: 0
  Block Id: 9345  linp Index: 86   Attributes: 3   Size: 24
  infomask: 0x0102 (HASVARWIDTH|XMIN_COMMITTED) 

  1fb8: 14e03f05 16e03f05 00000000 00008124  ..?...?........$
  1fc8: 56000300 02011800 01000000 43363134  V...........C614
  1fd8: 62653439 31616339 65356636 64633136  be491ac9e5f6dc16
  1fe8: 35653065 31323162 36316563 33000000  5e0e121b61ec3...
  1ff8: 791cce69 7ced0100                    y..i|...        

COPY: 1 614be491ac9e5f6dc165e0e121b61ec3        2017-03-12 00:26:23.553657
 Item   2 -- Length:   72  Offset: 8048 (0x1f70)  Flags: NORMAL
  XMIN: 88072212  XMAX: 0  CID|XVAC: 0
  Block Id: 0  linp Index: 2   Attributes: 3   Size: 24
  infomask: 0x0902 (HASVARWIDTH|XMIN_COMMITTED|XMAX_INVALID) 

  1f70: 14e03f05 00000000 00000000 00000000  ..?.............
  1f80: 02000300 02091800 02000000 43383335  ............C835
  1f90: 39653064 31623462 61323261 64336139  9e0d1b4ba22ad3a9
  1fa0: 65386634 38316231 61633336 31000000  e8f481b1ac361...
  1fb0: df1cce69 7ced0100                    ...i|...        

COPY: 2 8359e0d1b4ba22ad3a9e8f481b1ac361        2017-03-12 00:26:23.553759
......

为了得到记录,需要提供一下字段类型LIST,必须保证与表结构一致

-> pg_filedump -D int,text,timestamp ./173369|less  
  
*******************************************************************  
* PostgreSQL File/Block Formatted Dump Utility - Version 9.6.0  
*  
* File: ./173369  
* Options used: -D int,text,timestamp   
*  
* Dump created on: Sun Mar 12 00:31:25 2017  
*******************************************************************  
  
Block    0 ********************************************************  
<Header> -----  
 Block Offset: 0x00000000         Offsets: Lower     452 (0x01c4)  
 Block: Size 8192  Version    4            Upper     488 (0x01e8)  
 LSN:  logid     61 recoff 0xe69d6490      Special  8192 (0x2000)  
 Items:  107                      Free Space:   36  
 Checksum: 0x0000  Prune XID: 0x00000000  Flags: 0x0000 ()  
 Length (including item array): 452  
  
<Data> ------   
 Item   1 -- Length:   72  Offset: 8120 (0x1fb8)  Flags: NORMAL  
COPY: 1 614be491ac9e5f6dc165e0e121b61ec3        2017-03-12 00:26:23.553657  
 Item   2 -- Length:   72  Offset: 8048 (0x1f70)  Flags: NORMAL  
COPY: 2 8359e0d1b4ba22ad3a9e8f481b1ac361        2017-03-12 00:26:23.553759  
 Item   3 -- Length:   72  Offset: 7976 (0x1f28)  Flags: NORMAL  
COPY: 3 0dc8c441e91217897f994ae163510653        2017-03-12 00:26:23.553764  
..........  

COPY得到的就是使用-D提供的类型列表decode拼装的记录。

是不是可以从文件中DUMP数据了呢?莫急,还要看看掩码哦,否则你不知道这条记录是否为你需要的,因为它可能是DEAD TUPLE。

例子

-> pg_filedump -D int,text,timestamp -i -f ./173369|less  
  
COPY: 1 614be491ac9e5f6dc165e0e121b61ec3        2017-03-12 00:26:23.553657  
 Item   2 -- Length:   72  Offset: 8048 (0x1f70)  Flags: NORMAL  
  XMIN: 88072212  XMAX: 0  CID|XVAC: 0  
  Block Id: 0  linp Index: 2   Attributes: 3   Size: 24  
  infomask: 0x0902 (HASVARWIDTH|XMIN_COMMITTED|XMAX_INVALID)   

记录头的infomask解释

 

 

每条记录,头部都有infomask, infomask2掩码,掩码表示的意思,可以参考头文件

比如什么是DEAD TUPLE呢?

src/include/access/htup_details.h  
  
/*  
 * information stored in t_infomask:  
 */  
#define HEAP_HASNULL                    0x0001  /* has null attribute(s) */  
#define HEAP_HASVARWIDTH                0x0002  /* has variable-width attribute(s) */  
#define HEAP_HASEXTERNAL                0x0004  /* has external stored attribute(s) */  
#define HEAP_HASOID                             0x0008  /* has an object-id field */  
#define HEAP_XMAX_KEYSHR_LOCK   0x0010  /* xmax is a key-shared locker */  
#define HEAP_COMBOCID                   0x0020  /* t_cid is a combo cid */  
#define HEAP_XMAX_EXCL_LOCK             0x0040  /* xmax is exclusive locker */  
#define HEAP_XMAX_LOCK_ONLY             0x0080  /* xmax, if valid, is only a locker */  
  
 /* xmax is a shared locker */  
#define HEAP_XMAX_SHR_LOCK      (HEAP_XMAX_EXCL_LOCK | HEAP_XMAX_KEYSHR_LOCK)  
  
#define HEAP_LOCK_MASK  (HEAP_XMAX_SHR_LOCK | HEAP_XMAX_EXCL_LOCK | \  
                                                 HEAP_XMAX_KEYSHR_LOCK)  
#define HEAP_XMIN_COMMITTED             0x0100  /* t_xmin committed */  
#define HEAP_XMIN_INVALID               0x0200  /* t_xmin invalid/aborted */  
#define HEAP_XMIN_FROZEN                (HEAP_XMIN_COMMITTED|HEAP_XMIN_INVALID)  
#define HEAP_XMAX_COMMITTED             0x0400  /* t_xmax committed */  
#define HEAP_XMAX_INVALID               0x0800  /* t_xmax invalid/aborted */  
#define HEAP_XMAX_IS_MULTI              0x1000  /* t_xmax is a MultiXactId */  
#define HEAP_UPDATED                    0x2000  /* this is UPDATEd version of row */  
#define HEAP_MOVED_OFF                  0x4000  /* moved to another place by pre-9.0  
                                                                                 * VACUUM FULL; kept for binary  
                                                                                 * upgrade support */  
#define HEAP_MOVED_IN                   0x8000  /* moved from another place by pre-9.0  
                                                                                 * VACUUM FULL; kept for binary  
                                                                                 * upgrade support */  
#define HEAP_MOVED (HEAP_MOVED_OFF | HEAP_MOVED_IN)  
  
#define HEAP_XACT_MASK                  0xFFF0  /* visibility-related bits */  

观察deadtuple

postgres=# update digoal set info='new' where id=1;  
UPDATE 1  
postgres=# checkpoint;  
CHECKPOINT  

观察

pg_filedump -D int,text,timestamp -i -f ./173369|less  
  
 Item   1 -- Length:   72  Offset: 8120 (0x1fb8)  Flags: NORMAL  
  包含了xmax,说明是更新过的记录  
  XMIN: 88072212  XMAX: 88072214  CID|XVAC: 0  
  blockid表示记录指向,即新版本记录在哪个新数据块,Linp指新数据块的第几条记录。  
  Block Id: 9345  linp Index: 86   Attributes: 3   Size: 24  
  infomask 参考前面的头文件,解读  
  infomask: 0x0102 (HASVARWIDTH|XMIN_COMMITTED)   
  
  1fb8: 14e03f05 16e03f05 00000000 00008124  ..?...?........$  
  1fc8: 56000300 02011800 01000000 43363134  V...........C614  
  1fd8: 62653439 31616339 65356636 64633136  be491ac9e5f6dc16  
  1fe8: 35653065 31323162 36316563 33000000  5e0e121b61ec3...  
  1ff8: 791cce69 7ced0100                    y..i|...          
  
COPY: 1 614be491ac9e5f6dc165e0e121b61ec3        2017-03-12 00:26:23.553657  

查看新版本(编号为9345数据块,第86条记录)

pg_filedump -D int,text,timestamp -i -f -R 9345 ./173369|less  
  
 Item  86 -- Length:   40  Offset: 2032 (0x07f0)  Flags: NORMAL  
  XMIN: 88072214  XMAX: 0  CID|XVAC: 0  
  Block Id: 9345  linp Index: 86   Attributes: 3   Size: 24  
  infomask: 0x2802 (HASVARWIDTH|XMAX_INVALID|UPDATED)   
  
  07f0: 16e03f05 00000000 00000000 00008124  ..?............$  
  0800: 56000300 02281800 01000000 096e6577  V....(.......new  
  0810: 791cce69 7ced0100                    y..i|...          
  
COPY: 1 new     2017-03-12 00:26:23.553657  

PostgreSQL数据块的简介

对于数据文件的组织形式,可以参考头文件

src/include/storage

/*  
 * BlockNumber:  
 *  
 * each data file (heap or index) is divided into postgres disk blocks  
 * (which may be thought of as the unit of i/o -- a postgres buffer  
 * contains exactly one disk block).  the blocks are numbered  
 * sequentially, 0 to 0xFFFFFFFE.  
 *  
 * InvalidBlockNumber is the same thing as P_NEW in buf.h.  
 *  
 * the access methods, the buffer manager and the storage manager are  
 * more or less the only pieces of code that should be accessing disk  
 * blocks directly.  
 */  
typedef uint32 BlockNumber;  
  
#define InvalidBlockNumber              ((BlockNumber) 0xFFFFFFFF)  
  
#define MaxBlockNumber                  ((BlockNumber) 0xFFFFFFFE)  

每个块内的组织,与对象类型有关,比如堆表,B-TREE,HASH等索引,TOAST, FSM等。

可以参考数据layout介绍

https://www.postgresql.org/docs/9.6/static/storage.html

也可以参考对应类型的头文件

阅读pg_filedump的源码,也有助于你对PostgreSQL存储构造的理解

不妨仔细阅读以下头文件

#include "access/gin_private.h"  
#include "access/gist.h"  
#include "access/hash.h"  
#include "access/htup.h"  
#include "access/htup_details.h"  
#include "access/itup.h"  
#include "access/nbtree.h"  
#include "access/spgist_private.h"  
#include "catalog/pg_control.h"  
#include "storage/bufpage.h"  

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