由于某些非技术方面的原因，我们也在搞一些开源数据库引入，替换商业数据库，于是瞄上了PostgreSQL。
PostgreSQL本身的技术不在这里做介绍，虽然国内PostgreSQL没有Mysql那么流行，但是搜索一下，还是能够找到不少PostgreSQL中文的一些技术资料， 其中PG的官方文档是最详尽且最有助于学习PG的：
最新的9.4版本的online doc：http://www.postgresql.org/docs/9.4/static/index.html
山东瀚高科技提供的中文翻译文档：http://www.highgo.com.cn/docs/docs90cn/
Oracle迁移到PostgreSQL：
比较流行的迁移工具 ora2pg： http://ora2pg.darold.net/config.html#testing
大致原理：
该工具使用perl写的， 主要迁移功能都由ora2pg.conf 这个参数文件控制，该参数文件定义源库Oracle和目标库的DSN，通过DBD::Oracle Perl 、 DBD::Pg Perl 的module连接到源库和目标库， 按照用户制定的参数，导出源库Oracle的相关对象结构（也可以连数据一起导），导入到目标库PG。 导入可以是在线的（导出脚本不落地直接导入PG），也可以先生成导出脚本到本地，手动修改复核后，再手动使用psql导入PG。
ora2pg命令行各参数使用也比较清晰明了， 支持各种导出导入选项，比如你可以只导某些schema或者对象，或者排除某些schema或者对象不导， 也可以什么都不做，只对源库做一个迁移PG的分析，出具一份报告等等。
具体使用方法，还是自己去实际尝试会比较好。
使用Ora2pg的方案将Oracle迁移至PG， 遇到的问题多少与源Oracle数据库有多少与PG不兼容的东西成正比。下面是我们遇到的问题简单总结：
应用程序里面sqlmap.xml 人工REVIEW时的问题发现：
| Oracle | PostgreSQL |
| dual表 | 没有dual表，可以直接select 1、select user、select xxx |
| 时间函数（sysdate) | current_date current_time current_timestamp |
| trunc | trunc/date trunc（时间截断函数） |
| sys_guid() | 有类似sys_guid的函数uuid_generate_v4，但需要安装，create extension “uuid-oosp”. |
| nvl | PG可以使用COALESCE |
| where rownum < … | select row_number() over() , * from XXXX或者limit |
PG导入ora2pg产生的迁移脚本时发现的问题：
| tables | DEFAULT Sys_guid(); session# serial# 字段 | DEFAULT uuid_generate_v4; 去掉# |
| partitions | 父表在tables中已创建，创建子表时，由于大小写问题提示找不到父表。 | 表名称区分大小写，继承父表时，大小写改为与父表相同。增加或减少分区要修改触发器函数。 |
| synonyms | 转换过来的语句类似如下： CREATE VIEW public.tablename AS SELECT * FROM owner.tablename SECURITY DEFINER; | PG中没有同义词，自动创建为视图，转换过来的视图名称与存在的表名相同，需要修改视图名称。 SECURITY DEFINER不能加到创建语句的后面，可通过授权来控制权限。 |
| packages | 1、PG中没有v$session.(oracle原来的packages里面大多有这个） select sid, serial# into v_sid, v_serial# from v$session 2、有些转换过来的语句顺序不正确，需要重构。 3、packages自动转换为function,且function会创建到以原来packages命名的schema下 | ora2pg会把Oracle里面的package header转换为同名的schema |
| procedures | 1、dbms_output.put_line(‘成功插入数据！’);–>RAISE NOTICE ‘%’,(‘成功插入数据！’); 2、 dbms_output.put_line(sqlerrm) — RAISE NOTICE ‘%’, sqlerrm; 3、表的子查询必须包围在圆括弧里并且必须赋予一个别名 4、start with connect by 递归查询在PG中WITH RECURSIVE | |
| views | 1、字符类型问题 2、递归查询没有转换成功 3、外连接中的“+”号没有转换 4、DECODE函数需要重构 5、COALESCE 函数返回值类型不匹配 | 1、字符类型需要调整。 2、start with connect by 递归查询在PG中WITH RECURSIVE 3、 (+)这样的外连接写法需要调整为SQL标准的 table1 [LEFT|RIGHT|FULL] OUTER JOIN table2 ON (…); 4、DECODE函数需要重构成(case when some_column = ‘some_value’ then ‘some_other_value’ when … then … else ‘some_default_value’ end ) as some_column; 5、COALESCE 函数返回值类型不匹配、需要类型转换。 |
等等。
可以看到直接将Oracle迁移到PostgreSQL，无论是应用层，还是数据库层面， 都还是有很多改写工作要做的。
由于有上述诸多问题，我们研究了一下号称为替换Oracle而生的EnterpriseDB（PostgreSQL的商业版）：
http://www.enterprisedb.com/products-services-training/products/documentation/enterpriseedition
EnterpriseDB的安装指引：
http://www.enterprisedb.com/docs/en/9.4/instguide/toc.html
EnterpriseDB的官方文档：
http://www.enterprisedb.com/docs/en/9.4/eeguide/toc.html
EnterpriseDB的Oracle迁移PG的工具Migration Toolkit使用指引：
http://www.enterprisedb.com/docs/en/9.4/migrate/toc.html
工具使用比较简单，简单配置一些参数接口， 迁移过程发现的问题相比ora2pg少了很多，但还是有一些：
例如EDB中没有function sys_connect_by_path函数、 oracle trigger语法里面的referencing new as new old as old等。
结论：
虽然EDB的Migration Toolkit这个迁移工具本身没有像ora2pg那么多灵活的迁移选项组合， 但是其功能基本满足迁移需求，而且重要的是由于EDB在PostgreSQL的基础上，外面包了一层，实现了很多Oracle的概念，例如前面提到的dual表、同义词、pkg、内建函数，甚至Oracle的分区表语法可以直接在EDB运行。所以，同样的源Oracle数据库，我们发现90%左右的都可以直接在目标EnterpriseDB运行了，只需要修改一少部分。
具体EnterpriseDB的兼容Oracle的清单，参考
所以，从节省成本与运维稳定两方面平衡考虑， 对于新建系统直接采用PostgreSQL，对于已有系统迁移到PostgreSQL，使用EnterpriseDB也不失为一个过渡期的较好选择。
附录：
ora2pg –help
Usage: ora2pg [-dhpqv –estimate_cost –dump_as_html] [–option value]
-a | –allow str : coma separated list of objects to allow from export.
Can be used with SHOW_COLUMN too.
-b | –basedir dir: Used to set the default output directory, where files
resulting from exports will be stored.
-c | –conf file : Used to set an alternate configuration file than the
default /etc/ora2pg/ora2pg.conf.
-d | –debug : Enable verbose output.
-e | –exclude str: coma separated list of objects to exclude from export.
Can be used with SHOW_COLUMN too.
-h | –help : Print this short help.
-i | –input file : File containing Oracle PL/SQL code to convert with
no Oracle database connection initiated.
-j | –jobs num : number of parallel process to send data to PostgreSQL.
-J | –copies num : number of parallel connection to extract data from Oracle.
-l | –log file : Used to set a log file. Default is stdout.
-L | –limit num : number of tuples extracted from Oracle and stored in
memory before writing, default: 10000.
-n | –namespace schema : Used to set the Oracle schema to extract from.
-o | –out file : Used to set the path to the output file where SQL will
be written. Default: output.sql in running directory.
-p | –plsql : Enable PLSQL to PLPSQL code conversion.
-P | –parallel num: Number of parallel tables to extract at the same time.
-q | –quiet : disable progress bar.
-s | –source DSN : Allow to set the Oracle DBI datasource.
-t | –type export: Used to set the export type. It will override the one
given in the configuration file (TYPE).
-u | –user name : Used to set the Oracle database connection user.
-v | –version : Show Ora2Pg Version and exit.
-w | –password pwd : Used to set the password of the Oracle database user.
–forceowner: if set to 1 force ora2pg to set tables and sequences owner
like in Oracle database. If the value is set to a username this
one will be used as the objects owner. By default it’s the user
used to connect to the Pg database that will be the owner.
–nls_lang code: use this to set the Oracle NLS_LANG client encoding.
–client_encoding code: Use this to set the PostgreSQL client encoding.
–view_as_table str: coma separated list of view to export as table.
–estimate_cost : activate the migration cost evalution with SHOW_REPORT
–cost_unit_value minutes: number of minutes for a cost evalution unit.
default: 5 minutes, correspond to a migration conducted by a
PostgreSQL expert. Set it to 10 if this is your first migration.
–dump_as_html : force ora2pg to dump report in HTML, used only with
SHOW_REPORT. Default is to dump report as simple text.
–init_project NAME: initialise a typical ora2pg project tree. Top directory
will be created under project base dir.
–project_base DIR : define the base dir for ora2pg project trees. Default
is current directory.
See full documentation at http://ora2pg.darold.net/ for more help or see manpage with ‘man ora2pg’.
EDB的Migration Toolkit：
runMTK.sh -help
Running EnterpriseDB Migration Toolkit (Build 48.0.1) …
EnterpriseDB Migration Toolkit (Build 48.0.1)
Usage: runMTK [-options] SCHEMA
If no option is specified, the complete schema will be imported.
where options include:
-helpDisplay the application command-line usage.
-versionDisplay the application version information.
-verbose [on|off] Display application log messages on standard output (default: on).
-schemaOnlyImport the schema object definitions only.
-dataOnlyImport the table data only. When -tables is in place, it imports data only for the selected tables. Note: If there are any FK constraints defined on target tables, use -truncLoad option along with this option.
-sourcedbtype db_type The -sourcedbtype option specifies the source database type. db_type may be one of the following values: mysql, oracle, sqlserver, sybase, postgresql, enterprisedb. db_type is case-insensitive. By default, db_type is oracle.
-targetdbtype db_type The -targetdbtype option specifies the target database type. db_type may be one of the following values: oracle, sqlserver, postgresql, enterprisedb. db_type is case-insensitive. By default, db_type is enterprisedb.
-allTablesImport all tables.
-tables LISTImport comma-separated list of tables.
-constraintsImport the table constraints.
-indexesImport the table indexes.
-triggersImport the table triggers.
-allViewsImport all Views.
-views LISTImport comma-separated list of Views.
-allProcsImport all stored procedures.
-procs LISTImport comma-separated list of stored procedures.
-allFuncsImport all functions.
-funcs LISTImport comma-separated list of functions.
-allPackagesImport all packages.
-packages LIST Import comma-separated list of packages.
-allSequencesImport all sequences.
-sequences LIST Import comma-separated list of sequences.
-targetSchema NAME Name of the target schema (default: target schema is named after source schema).
-allDBLinksImport all Database Links.
-allSynonymsIt enables the migration of all public and private synonyms from an Oracle database to an Advanced Server database. If a synonym with the same name already exists in the target database, the existing synonym will be replaced with the migrated version.
-allPublicSynonymsIt enables the migration of all public synonyms from an Oracle database to an Advanced Server database. If a synonym with the same name already exists in the target database, the existing synonym will be replaced with the migrated version.
-allPrivateSynonymsIt enables the migration of all private synonyms from an Oracle database to an Advanced Server database. If a synonym with the same name already exists in the target database, the existing synonym will be replaced with the migrated version.
-dropSchema [true|false] Drop the schema if it already exists in the target database (default: false).
-truncLoadIt disables any constraints on target table and truncates the data from the table before importing new data. This option can only be used with -dataOnly.
-safeModeTransfer data in safe mode using plain SQL statements.
-copyDelimiterSpecify a single character to be used as delimiter in copy command when loading table data. Default is \t
-batchSizeSpecify the Batch Size to be used by the bulk inserts. Valid values are 1-1000, default batch size is 1000, reduce if you run into Out of Memory exception
-cpBatchSize Specify the Batch Size in MB, to be used in the Copy Command. Valid value is > 0, default batch size is 8 MB
-fetchSize Specify fetch size in terms of number of rows should be fetched in result set at a time. This option can be used when tables contain millions of rows and you want to avoid out of memory errors.
-filterPropThe properties file that contains table where clause.
-skipFKConstSkip migration of FK constraints.
-skipCKConstSkip migration of Check constraints.
-ignoreCheckConstFilterBy default MTK does not migrate Check constraints and Default clauses from Sybase, use this option to turn off this filter.
-fastCopyBypass WAL logging to perform the COPY operation in an optimized way, default disabled.
-customColTypeMapping LISTUse custom type mapping represented by a semi-colon separated list, where each entry is specified using COL_NAME_REG_EXPR=TYPE pair. e.g. .*ID=INTEGER
-customColTypeMappingFile PROP_FILEThe custom type mapping represented by a properties file, where each entry is specified using COL_NAME_REG_EXPR=TYPE pair. e.g. .*ID=INTEGER
-offlineMigration [PATH] This performs offline migration and saves the DDL/DML scripts in files for a later execution. By default the script files will be saved under user home folder, if required follow -offlineMigration option with a custom path.
-logDir LOG_PATH Specify a custom path to save the log file. By default, on Linux the logs will be saved under folder $HOME/.enterprisedb/migration-toolkit/logs. In case of Windows logs will be saved under folder %HOMEDRIVE%%HOMEPATH%\.enterprisedb\migration-toolkit\logs.
-copyViaDBLinkOra This option can be used to copy data using dblink_ora COPY commad. This option can only be used in Oracle to EnterpriseDB migration mode.
-singleDataFileUse single SQL file for offline data storage for all tables. This option cannot be used in COPY format.
-allUsers Import all users and roles from the source database.
-users LIST Import the selected users/roles from the source database. LIST is a comma-separated list of user/role names e.g. -users MTK,SAMPLE
-allRules Import all rules from the source database.
-rules LIST Import the selected rules from the source database. LIST is a comma-separated list of rule names e.g. -rules high_sal_emp,low_sal_emp
-allGroups Import all groups from the source database.
-groups LIST Import the selected groups from the source database. LIST is a comma-separated list of group names e.g. -groups acct_emp,mkt_emp
-allDomains Import all domain, enumeration and composite types from the source database.
-domains LIST Import the selected domain, enumeration and composite types from the source database. LIST is a comma-separated list of domain names e.g. -domains d_email,d_dob, mood
-objecttypesImport the user-defined object types.
-replaceNullChar <CHAR> If null character is part of a column value, the data migration fails over JDBC protocol. This option can be used to replace null character with a user-specified character.
-importPartitionAsTable [LIST] Use this option to import Oracle Partitioned table as a normal table in EnterpriseDB. To apply the rule on a selected set of tables, follow the option by a comma-separated list of table names.
-enableConstBeforeDataLoad Use this option to re-enable constraints (and triggers) before data load. This is useful in the scenario when the migrated table is mapped to a partition table in EnterpriseDB.
-checkFunctionBodies [true|false] When set to false, it disables validation of the function body during function creation, this is to avoid errors if function contains forward references. Applicable when target database is Postgres/EnterpriseDB, default is true.
-retryCount VALUESpecify the number of re-attempts performed by MTK to migrate objects that failed due to cross-schema dependencies. The VALUE parameter should be greater than 0, default is 2.
-analyze It invokes ANALYZE operation against a target Postgres or Postgres Plus Advanced Server database. The ANALYZE collects statistics for the migrated tables that are utilized for efficient query plans.
-vacuumAnalyze It invokes VACUUM and ANALYZE operations against a target Postgres or Postgres Plus Advanced Server database. The VACUUM reclaims dead tuple storage whereas ANALYZE collects statistics for the migrated tables that are utilized for efficient query plans.
-loaderCount VALUESpecify the number of jobs (threads) to perform data load in parallel. The VALUE parameter should be greater than 0, default is 1.
-logFileSize VALUEIt represents the maximum file size limit (in MB) before rotating to a new log file, defaults to 50MB.
-logFileCount VALUEIt represents the number of files to maintain in log file rotation history, defaults to 20. Specify a value of zero to disable log file rotation.
-useOraCaseIt preserves the identifier case while migrating from Oracle, except for functions, procedures and packages unless identifier names are given in quotes.
-logBadSQLIt saves the DDL scripts for the objects that fail to migrate, in a .sql file in log folder.
-targetDBVersionIt represents the major.minor version of the target database. This option is applicable for offline migration mode and is used to validate certain migration options as per target db version [default is 9.4 for EnterpriseDB database].
Database Connection Information:
The application will read the connectivity information for the source and target database servers from toolkit.properties file.
Refer to MTK readme document for more information.
