创建现有ram表的mnesia disk_copies [英] Creating mnesia disk_copies of existing ram table

问题描述

我有一个完整的mnesia ram_copies-only数据库，但是在向某个节点添加disk_copy表时遇到问题。现在我做：

I have a complete mnesia ram_copies-only database but I am experiencing problems adding a disk_copy table to a node. At the moment I do:

1. 创建我所有的ram_copy表/节点

1. Create all my ram_copy tables/nodes

在disk_copy-to-be节点上启动mnesia。

Start mnesia on the disk_copy-to-be node.

一切似乎都按照计划（没有运行时错误），但是当我去pwd（）。目录和检查，没有反映我刚刚创建的表的文件。另外当我在节点上调用 mnesia：info（）时，没有disk_copy表，只有一个ram_copy模式。

Everything seems to go according to plan (no run-time errors), but when I go to the pwd(). directory and check, there is no file reflecting the table I just created. Also when I call mnesia:info() on the node, there are no disk_copy tables, only a ram_copy schema.

推荐答案

您是否可以检查运行db节点字段是否列出了您已启动的两个节点？
可能是你没有将第二个节点添加到mnesia集群。

Can you check that the field "running db nodes" lists both nodes that you have started ? It could be that you did not add the second node to the mnesia cluster.

所以如果你的第二个节点被称为BNode，那么在第一个节点上将按以下顺序运行这些命令：

So if your second node was called BNode, then on the first node you would run these commands in this order:

1) mnesia:change_config(extra_db_nodes, [BNode]).  
2) mnesia:add_table_copy(table, BNode, disc_copies).

第二：我想你应该创建模式（步骤3），然后再启动mnesia disk_copy-to-be节点（步骤2）。

Second: I think you should be creating the schema (step 3) before you start up mnesia on the disk_copy-to-be node (step 2).

这是我创建所需的模式：

假设你有2节点NodeA和NodeB。

确保在开始之前没有Mnesia目录已存在。

This is what I did to create the schema you require:
Lets assume you have 2 nodes NodeA and NodeB.
Make sure that there is no Mnesia dir already existing before you start this.

%% From NodeA, setup the A node
erl -sname a -setcookie cookie
mnesia:start().
mnesia:create_table(mytable, [{attributes, [field1, field2]}]).

%% From NodeB, setup the B node
erl -sname b -setcookie cookie
net_adm:ping(NodeA).
mnesia:create_schema([node()]).
mnesia:start().

%% From NodeA, Add the NodeB to the mnesia cluster
[BNode | _] = nodes().
mnesia:change_config(extra_db_nodes, [BNode]).

%% From NodeA, add NodeB as a disc copy
mnesia:add_table_copy(mytable, BNode, disc_copies).

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