eXtremeDB相关问题解答（2）

1，Howto set the XML policy? 如何设置xml的策略？ 参加下列各参数定义，下列的结果为默认设置 The policy switches ignore_autoid andignore_autooid, when set to value MCO_YES, cause the procedure to ignore values forfields of this type in the XM

1，Howto set the XML policy?

如何设置xml的策略？

参加下列各参数定义，下列的结果为默认设置

The policy switches ignore_autoid andignore_autooid, when set to value MCO_YES,

cause the procedure to ignore values forfields of this type in the XML stream and

mco_w_xml_create_object() will generate theid values for the newly created

objects just as if they were created bycalling the classname_new() function.

static mco_xml_policy_t default_xml_policy= {

MCO_NUM_DEC, /* int_base is decimal */

MCO_NUM_HEX, /* quad_base is hexadecimal */

MCO_TEXT_ASCII, /* text_coding (strings) are ASCII */

MCO_TEXT_BASE64, /* blob_coding is Base64 */

MCO_FLOAT_EXPONENT, /* float_format isexponential */

MCO_YES, /* text is indented */

MCO_NO, /* all fields must be present in */

/* the incoming XML */

MCO_YES, /* encode special chars (

MCO_YES, /* encode line feeds */

MCO_NO, /* encode national chars (> 127) */

MCO_YES /* truncate trailing spaces */

MCO_NO, /* don't use attributes */

MCO_YES, /* ignore autoid values in input */

MCO_YES /* ignore autooid values in input */

}

2， Ifmain node(who have the quatam of 1) of cluster(qrank1,0,0,0,0,0,0) is down,could the cluster select a new main node?

cluster(qrank1,0,0,0,0,0,0)节点是否在主节点宕机后自动找主节点

不会，集群成为两个独立的集群，都为0的节点不能更新数据库。

3， Whatdoes HA time-awareness mean?

HA的timeawareness是什么意思？

The required performance characteristics ofa channel are specified in terms of timeouts, thus the primary attribute of thechannel is its on-time reliability.

4， CouldeXtremeDB Create table dynamically?

支持动态创建数据表么？

不支持。

5， NULL could be supported in 4.5.?

4.5能否支持NULL。

4.5暂不支持，5.0支持。

6， Could regular expression supported in eXtremeDB sql?

Sql是否支持正则表达式。

不支持。

7， Whatis the status of read-write for the HA nodes when it is synchronizing(static,hot) ?

在进行同步（static或者hot）的主备节点读写状态如何？

Static the master is read only, back is notready.

Hot : the master 可读写，备用节点不可用

8， Isthere any limit for the databases created inner a single process?

单进程创建数据库数量是否有限制？

The databases are put into astatic array, 在编译时可以重新定义，除此之外没有限制，

9， 使用SQL引擎时，内存设置大小如何确定？多任务SQL引擎能否支持多任务（McoSqlSession）共享一个StaticAllocator，或者每个任务（McoSqlSession）使用一个自己的StaticAllocator

The amount of memory that the allocator grabs depends on each SQLstatement. The

requirement can vary from several kilobytes to several megabytes (thatmuch memory can be necessary to process queries that select large number ofrecords and, for example, sort them).

多个session共享一个，因为allocator是在Engine背景下工作。

10， 是否支持多核下使用，如何支持？

一般直接通过操作系统实现线程，进程自动调度。

11， mco_db_save/mco_db_load在实现上是否支持大小端转换，即在大端设备上save，然后在小端的PC机上load

可以