EDB*Plus的client_encoding问题

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[作者 高健@博客园  luckyjackgao@gmail.com]

我的PPAS下，edb数据库的Encoding是 UTF8：

edb=# \l
                                        List of databases
   Name    |    Owner     | Encoding |   Collate   |    Ctype    |       Access
privileges
-----------+--------------+----------+-------------+-------------+--------------
-----------------
 edb       | enterprisedb | UTF8     | en_US.UTF-8 | en_US.UTF-8 |
 postgres  | enterprisedb | UTF8     | en_US.UTF-8 | en_US.UTF-8 |
 template0 | enterprisedb | UTF8     | en_US.UTF-8 | en_US.UTF-8 | =c/enterprisedb              +
           |              |          |             |             | enterprisedb=CTc/enterprisedb
 template1 | enterprisedb | UTF8     | en_US.UTF-8 | en_US.UTF-8 | =c/enterprisedb              +
           |              |          |             |             | enterprisedb=CTc/enterprisedb
(4 rows)

edb=# 。

而我在postgresql.conf里面去设置 client_encoding，无论如何也无法生效。

client_encoding = sql_ascii             # actually, defaults to database
                                        # encoding

重新启动后也不行：

edb=# show client_encoding;
 client_encoding
-----------------
 UTF8
(1 row)

edb=# 

也就是说，client_encoding的值，就算是设置了，也未必起作用。

查看社区版PostgreSQL的源代码作参考，看看是为何：

当我用psql连接到数据库时，CheckMyDatabase函数就会被执行。

我注意到其中的这一段：

    /* If we have no other source of client_encoding, use server encoding */
    SetConfigOption("client_encoding", GetDatabaseEncodingName(),
                    PGC_BACKEND, PGC_S_DYNAMIC_DEFAULT); 

在准备client_encoding的时候，它用了 GetDatabaseEncodingName()函数，来返回数据库的Encoding名称。

可以认为，其实postgresql.conf里的 client_encoding的设定是没有用处的，因为内部运算的时候直接拿来了所连接的数据库的Encoding。也可以说，client_encoding是一个历史遗留问题，是PostgreSQL的开发者的失误造成的！

/*
 * CheckMyDatabase -- fetch information from the pg_database entry for our DB
 */
static void
CheckMyDatabase(const char *name, bool am_superuser)
{                                    

    HeapTuple    tup;
    Form_pg_database dbform;
    char       *collate;
    char       *ctype;                            

    /* Fetch our pg_database row normally, via syscache */
    tup = SearchSysCache1(DATABASEOID, ObjectIdGetDatum(MyDatabaseId));
    if (!HeapTupleIsValid(tup))
        elog(ERROR, "cache lookup failed for database %u", MyDatabaseId);
    dbform = (Form_pg_database) GETSTRUCT(tup);                                

    /* This recheck is strictly paranoia */
    if (strcmp(name, NameStr(dbform->datname)) != )
        ereport(FATAL,
                (errcode(ERRCODE_UNDEFINED_DATABASE),
                 errmsg("database \"%s\" has disappeared from pg_database",
                        name),
                 errdetail("Database OID %u now seems to belong to \"%s\".",
                           MyDatabaseId, NameStr(dbform->datname))));            

    /*
     * Check permissions to connect to the database.
     * These checks are not enforced when in standalone mode, so that there is
     * a way to recover from disabling all access to all databases, for
     * example "UPDATE pg_database SET datallowconn = false;".
     *
     * We do not enforce them for autovacuum worker processes either.
     */
    if (IsUnderPostmaster && !IsAutoVacuumWorkerProcess())
    {
        /*
         * Check that the database is currently allowing connections.
         */
        if (!dbform->datallowconn)
            ereport(FATAL,
                    (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
             errmsg("database \"%s\" is not currently accepting connections",
                    name)));                

        /*
         * Check privilege to connect to the database.    (The am_superuser test
         * is redundant, but since we have the flag, might as well check it
         * and save a few cycles.)
         */
        if (!am_superuser &&
            pg_database_aclcheck(MyDatabaseId, GetUserId(),
                                 ACL_CONNECT) != ACLCHECK_OK)
            ereport(FATAL,
                    (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                     errmsg("permission denied for database \"%s\"", name),
                     errdetail("User does not have CONNECT privilege.")));                

        /*
         * Check connection limit for this database.
         *
         * There is a race condition here --- we create our PGPROC before
         * checking for other PGPROCs.    If two backends did this at about the
         * same time, they might both think they were over the limit, while
         * ideally one should succeed and one fail.  Getting that to work
         * exactly seems more trouble than it is worth, however; instead we
         * just document that the connection limit is approximate.
         */
        if (dbform->datconnlimit >=  &&
            !am_superuser &&
            CountDBBackends(MyDatabaseId) > dbform->datconnlimit)
            ereport(FATAL,
                    (errcode(ERRCODE_TOO_MANY_CONNECTIONS),
                     errmsg("too many connections for database \"%s\"",
                            name)));
    }                                

    /*
     * OK, we're golden.  Next to-do item is to save the encoding info out of
     * the pg_database tuple.
     */
    SetDatabaseEncoding(dbform->encoding);
    /* Record it as a GUC internal option, too */
    SetConfigOption("server_encoding", GetDatabaseEncodingName(),
                    PGC_INTERNAL, PGC_S_OVERRIDE);                

    /* If we have no other source of client_encoding, use server encoding */
    SetConfigOption("client_encoding", GetDatabaseEncodingName(),
                    PGC_BACKEND, PGC_S_DYNAMIC_DEFAULT);                

    /* assign locale variables */
    collate = NameStr(dbform->datcollate);
    ctype = NameStr(dbform->datctype);                                

    if (pg_perm_setlocale(LC_COLLATE, collate) == NULL)
        ereport(FATAL,
            (errmsg("database locale is incompatible with operating system"),
             errdetail("The database was initialized with LC_COLLATE \"%s\", "
                       " which is not recognized by setlocale().", collate),
             errhint("Recreate the database with another locale or install the missing locale.")));                        

    if (pg_perm_setlocale(LC_CTYPE, ctype) == NULL)
        ereport(FATAL,
            (errmsg("database locale is incompatible with operating system"),
             errdetail("The database was initialized with LC_CTYPE \"%s\", "
                       " which is not recognized by setlocale().", ctype),
             errhint("Recreate the database with another locale or install the missing locale.")));                        

    /* Make the locale settings visible as GUC variables, too */
    SetConfigOption("lc_collate", collate, PGC_INTERNAL, PGC_S_OVERRIDE);
    SetConfigOption("lc_ctype", ctype, PGC_INTERNAL, PGC_S_OVERRIDE);                                

    /* Use the right encoding in translated messages */
    #ifdef ENABLE_NLS
    pg_bind_textdomain_codeset(textdomain(NULL));
    #endif                                

    ReleaseSysCache(tup);           

}                                    

[作者 高健@博客园  luckyjackgao@gmail.com]

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磨砺技术珠矶，践行数据之道，追求卓越价值