PostgreSQL 扩展之 WalMiner
开源软件联盟PostgreSQL分会约 17 分钟WalMiner是从PostgreSQL的WAL(write ahead logs)日志的解析工具，旨在挖掘wal日志所有的有用信息，从而提供PG的数据恢复支持，3.0支持PostgreSQL10及其以上版本（pg14.2版本暂不支持，已与作者沟通）。
WalMiner可以从waL日志中解析出SQL，包括DML和少量DDL，与传统的logical decode插件相比，walminer不要求logical日志级别且解析方式较为灵活。
当数据库被执行了TRUNCATE等不被wal记录的数据清除操作，或者发生磁盘页损坏，可以使用此功能从wal日志中搜索数据，以期尽量挽回数据，达到数据页挽回的效果。
PostgreSQL版本：13.6
WalMiner 版本：3.0
安装部署
获取软件
--下载(由于3.0暂时没有release，直接下载master包即可)
wget https://gitee.com/movead/XLogMiner/repository/archive/master.zip
--将WalMiner放到数据库源码的contrib目录下,并给777权限
# pwd
/opt/software/postgresql-13.6/contrib
# ll |grep -i WalMiner
drwxrwxrwx 8777 root 4096Mar1514:31WalMiner
编译安装
--编译
# make && make install
--安装
postgres=# \dx
List of installed extensions
Name|Version|Schema|Description
--------------------+---------+------------+------------------------------------------------------------------------
pg_stat_statements |1.8|public| track planning and execution statistics of all SQL statements executed
plpgsql |1.0| pg_catalog | PL/pgSQL procedural language
(2 rows)
postgres=#select*from pg_available_extensions()where name='walminer';
name | default_version | comment
----------+-----------------+--------------------
walminer |3.0| analyse wal to SQL
(1 row)
postgres=# create extension walminer;
CREATE EXTENSION
postgres=# \dx
List of installed extensions
Name|Version|Schema|Description
--------------------+---------+------------+------------------------------------------------------------------------
pg_stat_statements |1.8|public| track planning and execution statistics of all SQL statements executed
plpgsql |1.0| pg_catalog | PL/pgSQL procedural language
walminer |3.0|public| analyse wal to SQL
(3 rows)
postgres=# \df walminer*
List of functions
Schema|Name|Result data type |Argument data types |Type
--------+----------------------------+------------------+-----------------------------------------------------------------------------------------------------------------------+------
public| walminer_all | text | reloid oid DEFAULT 0, tempresult boolean DEFAULT false| func
public| walminer_apply | text | startlsn pg_lsn, endlsn pg_lsn, fsearch boolean DEFAULT true, reloid oid DEFAULT 0, tempresult boolean DEFAULT false| func
public| walminer_build_dictionary | cstring | path cstring | func
public| walminer_by_lsn | text | startlsn pg_lsn, endlsn pg_lsn, fsearch boolean DEFAULT false, reloid oid DEFAULT 0, tempresult boolean DEFAULT false| func
public| walminer_by_time | text | starttime text, endtime text, fsearch boolean DEFAULT false, reloid oid DEFAULT 0, tempresult boolean DEFAULT false| func
public| walminer_by_xid | text | xid integer, fsearch boolean DEFAULT false, reloid oid DEFAULT 0, tempresult boolean DEFAULT false| func
public| walminer_contents_check |void|| func
public| walminer_debug_mode |boolean|| func
public| walminer_help | cstring || func
public| walminer_load_dictionary | cstring | path cstring | func
public| walminer_mrecords_inmemory | integer | records integer | func
public| walminer_regression_mode |boolean|| func
public| walminer_stop | cstring || func
public| walminer_table_avatar | cstring | tablename cstring, relfilenode oid | func
public| walminer_version | cstring || func
public| walminer_wal_add | cstring | path cstring | func
public| walminer_wal_list | SETOF record || func
public| walminer_wal_remove | cstring | path cstring | func
(18 rows)
postgres=# \df *wal2*
List of functions
Schema|Name|Result data type |Argument data types |Type
--------+----------------------+------------------+----------------------------------------------------------------------------------------------------------------------------+------
public| wal2sql | text | reloid oid DEFAULT 0, tempresult boolean DEFAULT false| func
public| wal2sql | text | startlsn pg_lsn, endlsn pg_lsn, fsearch boolean DEFAULT false, reloid oid DEFAULT 0, tempresult boolean DEFAULT false| func
public| wal2sql | text | starttime text, endtime text, fsearch boolean DEFAULT false, reloid oid DEFAULT 0, tempresult boolean DEFAULT false| func
public| wal2sql | text | xid integer, fsearch boolean DEFAULT false, reloid oid DEFAULT 0, tempresult boolean DEFAULT false| func
public| wal2sql_internal | text | starttime text, endtime text, startlsn pg_lsn, endlsn pg_lsn, xid integer, fsearch boolean, reloid oid, tempresult boolean| func
public| wal2sql_self_apply | integer || func
public| wal2sql_with_catalog |boolean|| func
public| wal2sql_with_ddl |boolean|| func
(8 rows)
测试场景
ps: 作者的码云中各测试场景都有非常详细的示例，大赞
--测试表准备
postgres=# show full_page_writes ;
full_page_writes
------------------
on
(1 row)
postgres=# create table walminer_t(id int,col1 varchar(8));
CREATE TABLE
postgres=# insert intowalminer_t values(1,'w1'),(2,'w2');
INSERT 02
postgres=#select*fromwalminer_t;
id | col1
----+------
1| w1
2| w2
(2 rows)
postgres=#select pg_current_wal_lsn();
pg_current_wal_lsn
--------------------
0/166EFD8
(1 row)
postgres=#select pg_walfile_name(pg_current_wal_lsn());
pg_walfile_name
--------------------------
000000010000000000000001
(1 row)
添加需要解析的wal文件
我们可以添加wal目录，也可以添加指定的wal文件（默认情况下此步骤可以省略，因为会直接加载当前数据字典和当前wal路径下的所有wal文件,但不建议省略）。
postgres=#select walminer_wal_add('/data/pgdata13/pg_wal');
walminer_wal_add
--------------------
1 file add success
(1 row)
postgres=#select walminer_wal_list();
walminer_wal_list
--------------------------------------------------
(/data/pgdata13/pg_wal/000000010000000000000001)
(1 row)
生成及加载数据字典
此步骤常用于异地实例解析wal文件的场景，需要源端数据库与目标数据库的版本相同，源端数据库需要添加walminer扩展后再生成数据字典，将数据字典传输到目标端数据库进行导入。
--源端数据库
create extension walminer;
select walminer_build_dictionary('/tmp/store_dictionary');
--目标端数据库
create extension walminer;
select walminer_load_dictionary('/tmp/store_dictionary');
开始解析wal文件
wal文件被解析之后，会被删除。
postgres=#select walminer_all();
NOTICE:Switch wal to 000000010000000000000001 on time 2022-03-1723:46:01.345277+08
walminer_all
---------------------
pg_minerwal success
(1 row)
postgres=#select walminer_wal_list();
ERROR: wal list has not been loaded or has been removed.
postgres=#
查看解析结果
walminer_contents是walminer自动生成的unlogged表，用来存储解析结果，在一次解析开始会先create或truncate此表，在表中我们看到这两条数据的xid、执行时间、执行操作、开始/结束lsn，甚至undo sql文本都写好了，很强大。
postgres=#select*from walminer_contents ;
sqlno | xid | topxid | sqlkind | minerd | timestamp | op_text | undo_text | complete | schema | relation | start_lsn | commit_lsn
-------+-----+--------+---------+--------+-------------------------------+---------------------------------------------------------+--------------------------------------------------------+----------+--------+------------+-----------+------------
1|499|0|1| t |2022-03-1723:39:08.891413+08| INSERT INTO public.walminer_t(id ,col1) VALUES(1,'w1')| DELETE FROM public.walminer_t WHERE id=1 AND col1='w1'| t |public|walminer_t|0/166EE10|0/166EEB8
2|499|0|1| t |2022-03-1723:39:08.891413+08| INSERT INTO public.walminer_t(id ,col1) VALUES(2,'w2')| DELETE FROM public.walminer_t WHERE id=2 AND col1='w2'| t |public|walminer_t|0/166EE50|0/166EEB8
(2 rows)
范围解析
生产上wal的数量可能非常多，解析全部wal文件可能不现实，walminer支持范围解析,这里做一下简单的展示。
基于时间范围解析
postgres=#select*from walminer_contents ;
sqlno | xid | topxid | sqlkind | minerd | timestamp | op_text | undo_text | complete | schema | relation | start_lsn | commit_lsn
-------+-----+--------+---------+--------+-------------------------------+-----------------------------------------------------------+----------------------------------------------------------+----------+--------+-------------+-----------+------------
1|499|0|1| t |2022-03-1723:39:08.891413+08| INSERT INTO public.walminer_t(id ,col1) VALUES(1,'w1')| DELETE FROM public.walminer_t WHERE id=1 AND col1='w1'| t |public|walminer_t|0/166EE10|0/166EEB8
2|499|0|1| t |2022-03-1723:39:08.891413+08| INSERT INTO public.walminer_t(id ,col1) VALUES(2,'w2')| DELETE FROM public.walminer_t WHERE id=2 AND col1='w2'| t |public|walminer_t|0/166EE50|0/166EEB8
1|506|0|1| t |2022-03-1800:43:31.689753+08| INSERT INTO public.walminer_t2(id ,col1) VALUES(1,'ww1')| DELETE FROM public.walminer_t2 WHERE id=1 AND col1='ww1'| t |public| walminer_t2 |0/16A0828|0/16A08D0
2|506|0|1| t |2022-03-1800:43:31.689753+08| INSERT INTO public.walminer_t2(id ,col1) VALUES(2,'ww2')| DELETE FROM public.walminer_t2 WHERE id=2 AND col1='ww2'| t |public| walminer_t2 |0/16A0868|0/16A08D0
(4 rows)
postgres=#select walminer_by_time('2022-03-17 23:39:00','2022-03-17 23:40:00');
NOTICE:Add wal from current pg_wal directory,donot suggest usethis way in produce
NOTICE:Switch wal to 000000010000000000000001 on time 2022-03-1800:46:44.177991+08
walminer_by_time
---------------------
pg_minerwal success
(1 row)
postgres=#select*from walminer_contents ;
sqlno | xid | topxid | sqlkind | minerd | timestamp | op_text | undo_text | complete | schema | relation | start_lsn | commit_lsn
-------+-----+--------+---------+--------+-------------------------------+---------------------------------------------------------+--------------------------------------------------------+----------+--------+------------+-----------+------------
1|499|0|1| t |2022-03-1723:39:08.891413+08| INSERT INTO public.walminer_t(id ,col1) VALUES(1,'w1')| DELETE FROM public.walminer_t WHERE id=1 AND col1='w1'| t |public|walminer_t|0/166EE10|0/166EEB8
2|499|0|1| t |2022-03-1723:39:08.891413+08| INSERT INTO public.walminer_t(id ,col1) VALUES(2,'w2')| DELETE FROM public.walminer_t WHERE id=2 AND col1='w2'| t |public|walminer_t|0/166EE50|0/166EEB8
(2 rows)
基于lsn范围解析
postgres=#select*from walminer_contents ;
sqlno | xid | topxid | sqlkind | minerd | timestamp | op_text | undo_text | complete | schema | relation | start_lsn | commit_lsn
-------+-----+--------+---------+--------+-------------------------------+-----------------------------------------------------------+----------------------------------------------------------+----------+--------+-------------+-----------+------------
1|499|0|1| t |2022-03-1723:39:08.891413+08| INSERT INTO public.walminer_t(id ,col1) VALUES(1,'w1')| DELETE FROM public.walminer_t WHERE id=1 AND col1='w1'| t |public|walminer_t|0/166EE10|0/166EEB8
2|499|0|1| t |2022-03-1723:39:08.891413+08| INSERT INTO public.walminer_t(id ,col1) VALUES(2,'w2')| DELETE FROM public.walminer_t WHERE id=2 AND col1='w2'| t |public|walminer_t|0/166EE50|0/166EEB8
1|506|0|1| t |2022-03-1800:43:31.689753+08| INSERT INTO public.walminer_t2(id ,col1) VALUES(1,'ww1')| DELETE FROM public.walminer_t2 WHERE id=1 AND col1='ww1'| t |public| walminer_t2 |0/16A0828|0/16A08D0
2|506|0|1| t |2022-03-1800:43:31.689753+08| INSERT INTO public.walminer_t2(id ,col1) VALUES(2,'ww2')| DELETE FROM public.walminer_t2 WHERE id=2 AND col1='ww2'| t |public| walminer_t2 |0/16A0868|0/16A08D0
(4 rows)
postgres=#select walminer_by_lsn('0/16A0828','0/16A08D0');
NOTICE:Add wal from current pg_wal directory,donot suggest usethis way in produce
NOTICE:Switch wal to 000000010000000000000001 on time 2022-03-1800:50:12.706725+08
walminer_by_lsn
---------------------
pg_minerwal success
(1 row)
postgres=#select*from walminer_contents ;
sqlno | xid | topxid | sqlkind | minerd | timestamp | op_text | undo_text | complete | schema | relation | start_lsn | commit_lsn
-------+-----+--------+---------+--------+-------------------------------+-----------------------------------------------------------+----------------------------------------------------------+----------+--------+-------------+-----------+------------
1|506|0|1| t |2022-03-1800:43:31.689753+08| INSERT INTO public.walminer_t2(id ,col1) VALUES(1,'ww1')| DELETE FROM public.walminer_t2 WHERE id=1 AND col1='ww1'| t |public| walminer_t2 |0/16A0828|0/16A08D0
2|506|0|1| t |2022-03-1800:43:31.689753+08| INSERT INTO public.walminer_t2(id ,col1) VALUES(2,'ww2')| DELETE FROM public.walminer_t2 WHERE id=2 AND col1='ww2'| t |public| walminer_t2 |0/16A0868|0/16A08D0
(2 rows)
postgres=#
基于指定xid解析
postgres=#select*from walminer_contents ;
sqlno | xid | topxid | sqlkind | minerd | timestamp | op_text | undo_text | complete | schema | relation | start_lsn | commit_lsn
-------+-----+--------+---------+--------+-------------------------------+-----------------------------------------------------------+----------------------------------------------------------+----------+--------+-------------+-----------+------------
1|499|0|1| t |2022-03-1723:39:08.891413+08| INSERT INTO public.walminer_t(id ,col1) VALUES(1,'w1')| DELETE FROM public.walminer_t WHERE id=1 AND col1='w1'| t |public|walminer_t|0/166EE10|0/166EEB8
2|499|0|1| t |2022-03-1723:39:08.891413+08| INSERT INTO public.walminer_t(id ,col1) VALUES(2,'w2')| DELETE FROM public.walminer_t WHERE id=2 AND col1='w2'| t |public|walminer_t|0/166EE50|0/166EEB8
1|506|0|1| t |2022-03-1800:43:31.689753+08| INSERT INTO public.walminer_t2(id ,col1) VALUES(1,'ww1')| DELETE FROM public.walminer_t2 WHERE id=1 AND col1='ww1'| t |public| walminer_t2 |0/16A0828|0/16A08D0
2|506|0|1| t |2022-03-1800:43:31.689753+08| INSERT INTO public.walminer_t2(id ,col1) VALUES(2,'ww2')| DELETE FROM public.walminer_t2 WHERE id=2 AND col1='ww2'| t |public| walminer_t2 |0/16A0868|0/16A08D0
(4 rows)
postgres=#select walminer_by_xid('499');
NOTICE:Add wal from current pg_wal directory,donot suggest usethis way in produce
NOTICE:Switch wal to 000000010000000000000001 on time 2022-03-1800:52:29.379106+08
walminer_by_xid
---------------------
pg_minerwal success
(1 row)
postgres=#select*from walminer_contents ;
sqlno | xid | topxid | sqlkind | minerd | timestamp | op_text | undo_text | complete | schema | relation | start_lsn | commit_lsn
-------+-----+--------+---------+--------+-------------------------------+---------------------------------------------------------+--------------------------------------------------------+----------+--------+------------+-----------+------------
1|499|0|1| t |2022-03-1723:39:08.891413+08| INSERT INTO public.walminer_t(id ,col1) VALUES(1,'w1')| DELETE FROM public.walminer_t WHERE id=1 AND col1='w1'| t |public|walminer_t|0/166EE10|0/166EEB8
2|499|0|1| t |2022-03-1723:39:08.891413+08| INSERT INTO public.walminer_t(id ,col1) VALUES(2,'w2')| DELETE FROM public.walminer_t WHERE id=2 AND col1='w2'| t |public|walminer_t|0/166EE50|0/166EEB8
(2 rows)
范围精确解析
在范围解析的基础上，更加解析的信息更加精确（暂未看出普通解析与精确解析的区别）
select walminer_by_time(starttime, endtime,'true');
select walminer_by_lsn(startlsn, endlsn,'true');
select walminer_by_xid(xid,'true');
或
select wal2sql(starttime, endtime,'true');
select wal2sql(startlsn, endlsn,'true');
select wal2sql(xid,'true');
单表解析
通过指定reloid来解析指定的表
postgres=#select*from walminer_contents ;
sqlno | xid | topxid | sqlkind | minerd | timestamp | op_text | undo_text | complete | schema | relation | start_lsn | commit_lsn
-------+-----+--------+---------+--------+-------------------------------+-----------------------------------------------------------+----------------------------------------------------------+----------+--------+-------------+-----------+------------
1|499|0|1| t |2022-03-1723:39:08.891413+08| INSERT INTO public.walminer_t(id ,col1) VALUES(1,'w1')| DELETE FROM public.walminer_t WHERE id=1 AND col1='w1'| t |public|walminer_t|0/166EE10|0/166EEB8
2|499|0|1| t |2022-03-1723:39:08.891413+08| INSERT INTO public.walminer_t(id ,col1) VALUES(2,'w2')| DELETE FROM public.walminer_t WHERE id=2 AND col1='w2'| t |public|walminer_t|0/166EE50|0/166EEB8
1|506|0|1| t |2022-03-1800:43:31.689753+08| INSERT INTO public.walminer_t2(id ,col1) VALUES(1,'ww1')| DELETE FROM public.walminer_t2 WHERE id=1 AND col1='ww1'| t |public| walminer_t2 |0/16A0828|0/16A08D0
2|506|0|1| t |2022-03-1800:43:31.689753+08| INSERT INTO public.walminer_t2(id ,col1) VALUES(2,'ww2')| DELETE FROM public.walminer_t2 WHERE id=2 AND col1='ww2'| t |public| walminer_t2 |0/16A0868|0/16A08D0
(4 rows)
postgres=#select oid,relname from pg_class where relname='walminer_t';
oid | relname
-------+------------
16497|walminer_t
(1 row)
postgres=#select walminer_by_time('2022-03-17 23:39:00','2022-03-18 01:40:00','true','16497');
NOTICE:Add wal from current pg_wal directory,donot suggest usethis way in produce
NOTICE:Switch wal to 000000010000000000000001 on time 2022-03-1801:01:57.94789+08
walminer_by_time
---------------------
pg_minerwal success
(1 row)
postgres=#select*from walminer_contents ;
sqlno | xid | topxid | sqlkind | minerd | timestamp | op_text | undo_text | complete | schema | relation | start_lsn | commit_lsn
-------+-----+--------+---------+--------+-------------------------------+---------------------------------------------------------+--------------------------------------------------------+----------+--------+------------+-----------+------------
1|499|0|1| t |2022-03-1723:39:08.891413+08| INSERT INTO public.walminer_t(id ,col1) VALUES(1,'w1')| DELETE FROM public.walminer_t WHERE id=1 AND col1='w1'| t |public|walminer_t|0/166EE10|0/166EEB8
2|499|0|1| t |2022-03-1723:39:08.891413+08| INSERT INTO public.walminer_t(id ,col1) VALUES(2,'w2')| DELETE FROM public.walminer_t WHERE id=2 AND col1='w2'| t |public|walminer_t|0/166EE50|0/166EEB8
(2 rows)
替身解析
当我们执行drop 或者 truncate 操作后，数据库的数据字典中的relfilenode可能已经被移除，无法解析出原来wal中的一些内容，在知道旧表表结构的基础上，我们可以使用替身的解析方法。
postgres=#select*from walminer_contents ;
sqlno | xid | topxid | sqlkind | minerd | timestamp | op_text | undo_text | complete | schema | relation | start_lsn | commit_lsn
-------+-----+--------+---------+--------+-------------------------------+-----------------------------------------------------------+----------------------------------------------------------+----------+--------+-------------+-----------+------------
1|499|0|1| t |2022-03-1723:39:08.891413+08| INSERT INTO public.walminer_t(id ,col1) VALUES(1,'w1')| DELETE FROM public.walminer_t WHERE id=1 AND col1='w1'| t |public|walminer_t|0/166EE10|0/166EEB8
2|499|0|1| t |2022-03-1723:39:08.891413+08| INSERT INTO public.walminer_t(id ,col1) VALUES(2,'w2')| DELETE FROM public.walminer_t WHERE id=2 AND col1='w2'| t |public|walminer_t|0/166EE50|0/166EEB8
1|506|0|1| t |2022-03-1800:43:31.689753+08| INSERT INTO public.walminer_t2(id ,col1) VALUES(1,'ww1')| DELETE FROM public.walminer_t2 WHERE id=1 AND col1='ww1'| t |public| walminer_t2 |0/16A0828|0/16A08D0
2|506|0|1| t |2022-03-1800:43:31.689753+08| INSERT INTO public.walminer_t2(id ,col1) VALUES(2,'ww2')| DELETE FROM public.walminer_t2 WHERE id=2 AND col1='ww2'| t |public| walminer_t2 |0/16A0868|0/16A08D0
(4 rows)
postgres=#select pg_relation_filenode('walminer_t'::regclass);
pg_relation_filenode
----------------------
16497
(1 row)
postgres=# drop table walminer_t;
DROP TABLE
postgres=# create table walminer_n(id int,col1 varchar(8));
CREATE TABLE
postgres=#select walminer_table_avatar('walminer_n',16497);
walminer_table_avatar
------------------------------
MAP[walminer_n:16560]->16497
(1 row)
postgres=#select walminer_all();
NOTICE:Add wal from current pg_wal directory,donot suggest usethis way in produce
NOTICE:Switch wal to 000000010000000000000001 on time 2022-03-1801:11:32.466401+08
walminer_all
---------------------
pg_minerwal success
(1 row)
postgres=#select*from walminer_contents ;
sqlno | xid | topxid | sqlkind | minerd | timestamp | op_text | undo_text | complete | schema | relation | start_lsn | commit_lsn
-------+-----+--------+---------+--------+-------------------------------+-----------------------------------------------------------+----------------------------------------------------------+----------+--------+-------------+-----------+------------
1|499|0|1| t |2022-03-1723:39:08.891413+08| INSERT INTO public.walminer_n(id ,col1) VALUES(1,'w1')| DELETE FROM public.walminer_n WHERE id=1 AND col1='w1'| t |public| walminer_n |0/166EE10|0/166EEB8
2|499|0|1| t |2022-03-1723:39:08.891413+08| INSERT INTO public.walminer_n(id ,col1) VALUES(2,'w2')| DELETE FROM public.walminer_n WHERE id=2 AND col1='w2'| t |public| walminer_n |0/166EE50|0/166EEB8
1|506|0|1| t |2022-03-1800:43:31.689753+08| INSERT INTO public.walminer_t2(id ,col1) VALUES(1,'ww1')| DELETE FROM public.walminer_t2 WHERE id=1 AND col1='ww1'| t |public| walminer_t2 |0/16A0828|0/16A08D0
2|506|0|1| t |2022-03-1800:43:31.689753+08| INSERT INTO public.walminer_t2(id ,col1) VALUES(2,'ww2')| DELETE FROM public.walminer_t2 WHERE id=2 AND col1='ww2'| t |public| walminer_t2 |0/16A0868|0/16A08D0
(4 rows)
删除wal文件
只能删除wal文件，不能像添加一样直接删除整个目录。
postgres=#select walminer_wal_list();
walminer_wal_list
--------------------------------------------------
(/data/pgdata13/pg_wal/000000010000000000000001)
(1 row)
postgres=#select walminer_wal_remove('/data/pgdata13/pg_wal/');
ERROR:Argument can be file only, an not be a directory
postgres=#select walminer_wal_remove('/data/pgdata13/pg_wal/000000010000000000000001');
walminer_wal_remove
-----------------------
1 file remove success
(1 row)
postgres=#select walminer_wal_list();
ERROR: wal list has not been loaded or has been removed.
postgres=#
结束walminer
该函数作用为释放内存，结束日志分析。
postgres=#select walminer_stop();
walminer_stop
------------------
walminer stoped!
开发中的功能
开发中的功能暂不在这里展示，可以直接看作者网站
自apply解析
适用于主备切换，但是源主库部分wal日志未同步到新主库的场景，此种方法可以直接将结果解析到指定的表中。
select walminer_apply(startlsn, endlsn,'true', reloid);
DDL解析
这里分两部分，分别是系统表变化解析和普通DDL解析。
目前walminer支持解析系统表的变化。也就是说如果在PG执行了DDL语句，walminer可以分析出DDL语句引起的系统表的变化，系统表变化解析和DDL解析不共存，总是接受最新确定的状态。
--在执行解析之前，先执行如下语句，即可开启系统表解析功能
select wal2sql_with_catalog();
DDL解析
--在执行解析之前，先执行如下语句，即可开启DDL解析功能
select wal2sql_with_ddl();
数据页挽回
创建extension，创建数据地点，加载wal日志的方法与[SQL解析]中描述的方法一致。
select page_collect(relfilenode, reloid, pages);
relfilenode：需要解析的wal日志中的relfilenode
reloid：解析库中存在的表的OID，此命令将会将从wal中找到的page覆盖到reloid制定的表中
pages：是字符串类型，制定想要挽回的目标page。格式为'0,1,2,7'或者'all'。
结束语
这个插件现在的功能现在已经足够处理常规的误操作，达到闪回的效果，且此工具还在不断开发完善中，让我们一起期待一个更强大更完善的救火工具。