用python模仿bbed写了一个bbed for pg的脚本，简单的查看和修改字节都可以做到，你可以在这里下载到最新的版本。如果你不清楚这个脚本的功能，请不要轻易在生产环境使用它，这很危险。
使用环境：
1、linux
2、python 2.7
你可以通过$PGDATA环境变量找到数据文件的目录。
postgres=# show data_directory;
data_directory
----------------
/oracle/soft/pg_data
(1 row)
postgres=#
比如t1表的page
postgres=# select pg_relation_filepath('t1');
pg_relation_filepath
----------------------
base/13323/24706
(1 row)
postgres=#
然后编辑bbedp脚本下的file文件就可以开始了，目前仅支持单个文件
vi file
/oracle/soft/pg_data/base/13323/24706
这里你需要给x权限运行就可以了，为了效果就不要密码了。
postgres@whf307-> ./bbedp
Password:
BBEDP: Release 0.1.0.0.0 - Limited Production on Sat Nov 24 16:50:30 2018
Copyright (c) 2018, 2018, whf307 and/or its affiliates. All rights reserved.
************* !!! For PostgreSQL Internal Test only !!! ***************
BBEDP> help
set block [block_offset]
set count [bytes_to_display]
set offset [offset_to_dump]
map :map the struct
d :dump the offset
p :print offset
p PageHeaderData :to print the page header struct
p Linps :to print the linps
p linp[n] :to print the linp[n]
p Tuples: print all tupels
p tuples [n]:print the tuple n
p Pd_special : print pd_special
m /x aaaa offset bbbb :to modify the offset
exit :exit the program
BBEDP>
如果你了解bbed，那么help看一眼帮助就很容易上手bbedp了，你不了解bbed也没关系，脚本很简单，主要功能有查看page结构，dump字节，修改字节。
BBEDP> map
File: /oracle/soft/pg_data/base/13323/16428
Block: 0 offset: 0
-------------------------------------------------------------------
struct PageHeaderData , 24 bytes @0
struct Linps , 44 bytes @24
struct Tuples , 392 bytes @68
struct Pd_special , 0 bytes @8191
There are 11 tuples in the block
BBEDP>
默认从block 0开始，你可以set block到指定的block再开始
BBEDP> p PageHeaderData
struct PageHeaderData, 24 bytes @0
pd_lsn @0 0x0600000008e2a262
pd_checksum @8 0x0000
pd_flags @10 0x0000
pd_lower @12 0x4400
pd_upper @14 0x781e
pd_special @16 0x0020
pd_pagesize_version @18 0x0420
pd_prune_xid @20 0x33070000
BBEDP> p Linps
linp 1 @24 0x003c9fe0
-------------------------
lp_off : 8160
lp_flags : 1
lp_len : 30
linp 2 @28 0x3c9fc000
-------------------------
lp_off : 8128
lp_flags : 1
lp_len : 30
linp 3 @32 0x9fa0003c
-------------------------
lp_off : 8096
lp_flags : 1
lp_len : 28
...
BBEDP> p Tuples
tuple 1
-----------------------------------------------------
lp_off 8160 @24 0x003c9fe0
lp_flags 1 @24 0x003c9fe0
lp_len 30 @24 0x003c9fe0
t_xmin 1791 @8160 0xff060000
t_xmax 1843 @8164 0x33070000
t_field3 0 @8168 0x00000000
t_ctid (0,6) @8172 0x000000000600
t_infomask2 16387 @8178 0x0340
t_infomask 1795 @8180 0x0307
t_hoff 24 @8182 0x18
bits8 0b11 @8183 0x03
tupledata @8184 0x010000000578
tuple 2
-----------------------------------------------------
lp_off 8128 @28 0x3c9fc000
lp_flags 1 @28 0x3c9fc000
lp_len 30 @28 0x3c9fc000
t_xmin 1791 @8128 0xff060000
t_xmax 1843 @8132 0x33070000
t_field3 0 @8136 0x00000000
t_ctid (0,7) @8140 0x000000000700
t_infomask2 16387 @8146 0x0340
t_infomask 1795 @8148 0x0307
t_hoff 24 @8150 0x18
bits8 0b11 @8151 0x03
tupledata @8152 0x040000000578
...
当然，也可直接p
BBEDP> p PageHeaderData
struct PageHeaderData, 24 bytes @0
pd_lsn @0 0x0600000008e2a262
pd_checksum @8 0x0000
pd_flags @10 0x0000
pd_lower @12 0x4400
pd_upper @14 0x781e
pd_special @16 0x0020
pd_pagesize_version @18 0x0420
pd_prune_xid @20 0x33070000
BBEDP>
BBEDP> p 20
PageHeaderData.pd_checksum
------------------------------------------------
pd_prune_xid @20 0x33070000
BBEDP> p 44
IteamIdDatas
------------------------------------------------
linp6 @44 0x00440078
BBEDP> p 8188
Tuples
------------------------------------------------
tupledata @8188 0x0578
BBEDP>
p 指定行指针和tuple
BBEDP> p linp 1
linp1 @24 0xe09f3c
-------------------------
lp_off : 8160
lp_flags : 1
lp_len : 30
BBEDP> p tuple 1
tuple 1
-----------------------------------------------------
lp_off 8160 @24 0x003c9fe0
lp_flags 1 @24 0x003c9fe0
lp_len 30 @24 0x003c9fe0
t_xmin 1791 @8160 0xff060000
t_xmax 1843 @8164 0x33070000
t_field3 0 @8168 0x00000000
t_ctid (0,6) @8172 0x000000000600
t_infomask2 16387 @8178 0x0340
t_infomask 1795 @8180 0x0307
t_hoff 24 @8182 0x18
bits8 0b11 @8183 0x03
tupledata @8184 0x010000000578
BBEDP>
BBEDP> p PageHeaderData
struct PageHeaderData, 24 bytes @0
pd_lsn @0 0x0600000008e2a262
pd_checksum @8 0x0000
pd_flags @10 0x0000
pd_lower @12 0x4400
pd_upper @14 0x781e
pd_special @16 0x0020
pd_pagesize_version @18 0x0420
pd_prune_xid @20 0x33070000
BBEDP> d
File: /oracle/soft/pg_data/base/13323/16428
Block: 0 Offsets: 0 to 511
----------------------------------------------------------------------
06000000 08e2a262 00000000 4400781e 00200420 33070000 e09f3c00 c09f3c00
a09f3800 809f3c00 609f3c00 389f4800 109f4800 f09e4000 c89e4800 a09e4800
789e4800 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
<32 bytes per line>
BBEDP>
BBEDP> set offset 18
OFFSET 18
BBEDP> set count 32
COUNT 32
BBEDP> d
File: /oracle/soft/pg_data/base/13323/16428
Block: 0 Offsets: 18 to 49
----------------------------------------------------------------------
04203307 0000e09f 3c00c09f 3c00a09f 3800809f 3c00609f 3c00389f 4800109f
<32 bytes per line>
BBEDP>
postgres=# select * from t5;
id | name
----+------------
1 | x
2 | xx
3 | xxx
(3 rows)
postgres=# delete from t5 where id=3;
DELETE 1
postgres=# checkpoint;
CHECKPOINT
postgres=# select * from t5;
id | name
----+------------
1 | x
2 | xx
(2 rows)
postgres=#
postgres=# checkpoint;
CHECKPOINT
postgres=#
postgres=# select pg_relation_filepath('t5');
pg_relation_filepath
----------------------
base/13323/24714
(1 row)
postgres=#
postgres@whf307-> vi file
/oracle/soft/pg_data/base/13323/24714
postgres@whf307-> ./bbedp
Password:
BBEDP: Release 0.1.0.0.0 - Limited Production on Sat Nov 24 17:15:45 2018
Copyright (c) 2018, 2018, whf307 and/or its affiliates. All rights reserved.
************* !!! For PostgreSQL Internal Test only !!! ***************
BBEDP> map
File: /oracle/soft/pg_data/base/13323/24714
Block: 0 offset: 0
-------------------------------------------------------------------
struct PageHeaderData , 24 bytes @0
struct Linps , 12 bytes @24
struct Tuples , 120 bytes @36
struct Pd_special , 0 bytes @8191
There are 3 tuples in the block
BBEDP>
BBEDP> p Tuples
tuple 1
-----------------------------------------------------
lp_off 8152 @24 0x004e9fd8
lp_flags 1 @24 0x004e9fd8
lp_len 39 @24 0x004e9fd8
t_xmin 1793 @8152 0x01070000
t_xmax 0 @8156 0x00000000
t_field3 0 @8160 0x00000000
t_ctid (0,1) @8164 0x000000000100
t_infomask2 2 @8170 0x0200
t_infomask 2818 @8172 0x020b
t_hoff 24 @8174 0x18
bits8 0b0 @8175 0x00
tupledata @8176 0x010000001778202020202020202020
tuple 2
-----------------------------------------------------
lp_off 8112 @28 0x4e9fb000
lp_flags 1 @28 0x4e9fb000
lp_len 39 @28 0x4e9fb000
t_xmin 1884 @8112 0x5c070000
t_xmax 0 @8116 0x00000000
t_field3 0 @8120 0x00000000
t_ctid (0,2) @8124 0x000000000200
t_infomask2 2 @8130 0x0200
t_infomask 2306 @8132 0x0209
t_hoff 24 @8134 0x18
bits8 0b0 @8135 0x00
tupledata @8136 0x020000001778782020202020202020
tuple 3
-----------------------------------------------------
lp_off 8072 @32 0x9f88004e
lp_flags 1 @32 0x9f88004e
lp_len 39 @32 0x9f88004e
t_xmin 1884 @8072 0x5c070000
t_xmax 1885 @8076 0x5d070000
t_field3 0 @8080 0x00000000
t_ctid (0,3) @8084 0x000000000300
t_infomask2 8194 @8090 0x0220
t_infomask 1282 @8092 0x0205
t_hoff 24 @8094 0x18
bits8 0b0 @8095 0x00
tupledata @8096 0x030000001778787820202020202020
BBEDP>
可以看到tuple3这里t_xmax不为空，可能被删了，我们修改找回来。
BBEDP> p tuple 3
tuple 3
-----------------------------------------------------
lp_off 8072 @32 0x9f88004e
lp_flags 1 @32 0x9f88004e
lp_len 39 @32 0x9f88004e
t_xmin 1884 @8072 0x5c070000
t_xmax 1885 @8076 0x5d070000
t_field3 0 @8080 0x00000000
t_ctid (0,3) @8084 0x000000000300
t_infomask2 8194 @8090 0x0220
t_infomask 1282 @8092 0x0205
t_hoff 24 @8094 0x18
bits8 0b0 @8095 0x00
tupledata @8096 0x030000001778787820202020202020
BBEDP> m /x 0000 offset 8076
BBEDP> m /x 0200 offset 8090
BBEDP> m /x 0209 offset 8092
BBEDP> p tuple 3
tuple 3
-----------------------------------------------------
lp_off 8072 @32 0x9f88004e
lp_flags 1 @32 0x9f88004e
lp_len 39 @32 0x9f88004e
t_xmin 1884 @8072 0x5c070000
t_xmax 0 @8076 0x00000000
t_field3 0 @8080 0x00000000
t_ctid (0,3) @8084 0x000000000300
t_infomask2 2 @8090 0x0200
t_infomask 2306 @8092 0x0209
t_hoff 24 @8094 0x18
bits8 0b0 @8095 0x00
tupledata @8096 0x030000001778787820202020202020
BBEDP>
可以看到已经改过来了，重启实例刷新shared buffer
postgres@whf307-> pg_ctl stop -m fast
waiting for server to shut down.... done
server stopped
postgres@whf307-> pg_ctl start -l ./server.log
server starting
postgres@whf307-> psql
psql (9.6.9)
Type "help" for help.
postgres=# select * from t5;
id | name
----+------------
1 | x
2 | xx
3 | xxx
(3 rows)
你可以exit来退出程序
不一定有用，但是好玩！