oracle_fdw使用记录

通过oracle_fdw可以访问oracle中的一些表和视图，也可以进行修改，尤其是给比较复杂的系统使用非常方便。

1.安装oracle_fdw:

1）编译安装oracle_fdw之前，需要安装Oracle的客户端程序;下载地址：http://www.oracle.com/technetwork/database/database-technologies/instant-client/overview/index.html

主要是sdk和basic：

instantclient-basic-linux.x64-18.5.0.0.0dbru.zip

instantclient-sdk-linux.x64-18.5.0.0.0dbru.zip

2）下载地址：http://pgxn.org/dist/oracle_fdw/

unzip oracle_fdw-2.1.0.zip

cd oracle_fdw-2.1.0

3）配置环境变量：

[root@fce40690-0e46-4603-e80e-ca351bda31ec ~]# cat ora-env.sh

export ORACLE_HOME=/opt/oracle/instantclient

export OCI_LIB_DIR=$ORACLE_HOME

export OCI_INC_DIR=$ORACLE_HOME/sdk/include

[root@fce40690-0e46-4603-e80e-ca351bda31ec ~]# cat pg-env.sh

[ -f /etc/profile ] && source /etc/profile

PGDATA=/var/lib/pgsql/11/data

export PGDATA

# If you want to customize your settings,

# Use the file below. This is not overridden

# by the RPMS.

[ -f /var/lib/pgsql/.pgsql_profile ] && source /var/lib/pgsql/.pgsql_profile

export PGHOME=/usr/pgsql-11/

export LD_LIBRARY_PATH=$PGHOME/lib:$LD_LIBRARY_PATH:/opt/oracle/instantclient/

export PATH=$PATH:$PGHOME/bin

4）编译安装：

make && make install

2.配置oracle数据库tnsnames.ora，可以将Oracle那边的对应文件拷贝过来即可，注意里面的IP地址：

[postgres@fce40690-0e46-4603-e80e-ca351bda31ec ~]$ cat /opt/oracle/instantclient/network/admin/tnsnames.ora

# tnsnames.ora Network Configuration File: /ora/oracle/product/11.2.0/dbhome_1/network/admin/tnsnames.ora

# Generated by Oracle configuration tools.

ORCL =

(DESCRIPTION =

(ADDRESS = (PROTOCOL = TCP)(HOST = 10.9.10.236)(PORT = 1521))

(CONNECT_DATA =

(SERVER = DEDICATED)

(SERVICE_NAME = orcl)

)

3.创建外部表

1）创建server：

create server oracle_test foreign data wrapper oracle_fdw options(dbserver 'ORCL');

2）创建mapping：

create user mapping for postgres server oracle_test options (user 'oracle', password 'oracle');

3）创建外部表：

CREATE FOREIGN TABLE test(

id int

) SERVER oracle_test options (schema 'ORACLE', table 'TEST');

4）检查：

postgres=# select oracle_diag();

oracle_diag

-------------------------------------------------------------

oracle_fdw 2.1.0, PostgreSQL 11.2, Oracle client 18.5.0.0.0

(1 row)

5）查询：

postgres=# select * from test;

----

(1 row)

4.在查询时如果提示错误：ORA-12154

postgres=# select * from test;

ERROR: connection for foreign table "test" cannot be established

DETAIL: ORA-12154: TNS:could not resolve the connect identifier specified

1）确认环境变量是否在postgres用户下设置

2）确认oracle的instantclient是否有postgres的访问权限

5.外部表的一些配置选项：

Foreign table options

table (required)

The Oracle table name. This name must be written exactly as it occurs in Oracle's system catalog, so normally consist of uppercase letters only.

To define a foreign table based on an arbitrary Oracle query, set this option to the query enclosed in parentheses, e.g.

OPTIONS (table '(SELECT col FROM tab WHERE val = ''string'')')
Do not set the schema option in this case.
INSERT, UPDATE and DELETE will work on foreign tables defined on simple queries; if you want to avoid that (or confusing Oracle error messages for more complicated queries), use the table option readonly.

schema (optional)

The table's schema (or owner). Useful to access tables that do not belong to the connecting Oracle user. This name must be written exactly as it occurs in Oracle's system catalog, so normally consist of uppercase letters only.

max_long (optional, defaults to "32767")

The maximal length of any LONG or LONG RAW columns in the Oracle table. Possible values are integers between 1 and 1073741823 (the maximal size of a bytea in PostgreSQL). This amount of memory will be allocated at least twice, so large values will consume a lot of memory.
If max_long is less than the length of the longest value retrieved, you will receive the error message ORA-01406: fetched column value was truncated.

readonly (optional, defaults to "false")

INSERT, UPDATE and DELETE is only allowed on tables where this option is not set to yes/on/true. Since these statements can only be executed from PostgreSQL 9.3 on, setting this option has no effect on earlier versions. It might still be a good idea to set it in PostgreSQL 9.2 and earlier on tables that you do not wish to be changed, to be prepared for an upgrade to PostgreSQL 9.3 or later.

sample_percent (optional, defaults to "100")

This option only influences ANALYZE processing and can be useful to ANALYZE very large tables in a reasonable time.

The value must be between 0.000001 and 100 and defines the percentage of Oracle table blocks that will be randomly selected to calculate PostgreSQL table statistics. This is accomplished using the SAMPLE BLOCK (x) clause in Oracle.

ANALYZE will fail with ORA-00933 for tables defined with Oracle queries and may fail with ORA-01446 for tables defined with complex Oracle views.

prefetch (optional, defaults to "200")

Sets the number of rows that will be fetched with a single round-trip between PostgreSQL and Oracle during a foreign table scan. This is implemented using Oracle row prefetching. The value must be between 0 and 10240, where a value of zero disables prefetching.

Higher values can speed up performance, but will use more memory on the PostgreSQL server.

但是在实际操作过程中，往往会遇到oracle中通dblink访问其他数据库创建的synonym（同义词），这些同义词包括了表、视图、序列、包，那么是否可以通过oracle_fdw来访问序列和包呢？

oracle_fdw的外部表可以是一个SQL语句，基于此，下面做一些实验：

6.通过oracle_fdw访问oracle的序列、包和函数等对象：

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