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关于连接 oracle 需要强调 connect string 的解释
上一篇 / 下一篇 2008-03-06 03:27:07 / 个人分类：Oracle Database
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feng_xin / 2008-03-21 14:00:05
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当使用连接串的时候, oracle走的是sqlnet通讯,通过TCP/IP与sqlnet的认证机制进行client/server方式的通讯.
当不使用连接串的时候，oracle使用的是unix的进程间IPC通讯机制. IPC---Inter-Process Communications
IPC可以通过管道或共享内存等进行通讯，IPC的通讯也有安全限制, 可参考如下资料.
Access Permission Modes - The 'ipc_perm' Structure
SysV IPC resources may be protected using access mode permissions, much like files and directories are protected by the Unix system. Each such resource has an owning user and an owning group. Permission modes define if and how processes belonging to different users in the system may access this resource. Permissions may be set separately for the owning user, for users from the owning group, and everyone else. permissions may be set for reading the resource (e.g. reading messages from a message queue), or writing to the resource (e.g. sending a message on a queue, changing the value of a semaphore). A structure of type 'ipc_perm', which is defined as follows:
struct ipc_perm
{
key_t key; /* key identifying the resource */
ushort uid; /* owner effective user ID and effective group ID */
ushort gid;
ushort cuid; /* creator effective user ID and effective group ID */
ushort cgid;
ushort mode; /* access modes */
ushort seq; /* sequence number */
};
These fields have the following meanings:
• key - the identifier of the resource this structure refers to.
• uid - effective user ID owning the resource.
• gid - effective group ID owning the resource.
• cuid - effective user ID that created the resource.
• cgid - effective group ID that created the resource.
• mode - access permission modes for the given resource. This is a bit field, with the lowest 9 bits denoting access flags, and are a bit-wise 'or' of the following (octal) values:
o 0400 - owning user may read from this resource.
o 0200 - owning user may write to this resource.
o 0040 - owning group may read from this resource.
o 0020 - owning group may write to this resource.
o 0004 - every other user may read from this resource.
o 0002 - every other user may write to this resource.
• seq - used to keep system-internal info about the resource. for further info, check your kernel's sources (you are working on a system with free access to its source code, right?).
Part of the SysV IPC API allows us to modify the access permissions for the resources. We will encounter them when discussing the different IPC methods.
