我从3.0降级到2.1.7后无法看到C * 2.1.7中的所有键空间 [英] Unable to see all keyspaces in C* 2.1.7 after I downgraded from 3.0 to 2.1.7

问题描述

我一直在使用Cassandra 2.1.7，由于某种原因，我升级到3.0.12，后来意识到一些依赖的应用程序不能在3.0.12上运行，所以我降级了，并像以前一样使用C * 2.1.7使用之前。但是现在我看不到C *中的键空间。 （仅供参考：两个C * yaml文件中的数据目录都相同）

I've been using Cassandra 2.1.7 and For some reason I upgraded to 3.0.12 and later realized that some dependent apps won't work with 3.0.12 and I downgraded and using C* 2.1.7 as I was using before. But Now I'm not able to see Keyspaces in C*. (Just FYI: Data directory is same in both C*yaml files)

我需要进行任何更改吗？

Do I have to make any changes?

感谢您的帮助。

推荐答案

如果您尚未备份，则无需担心，因为C * 3.0不会在升级后删除较旧的数据库

以下是我为保留数据所做的操作：
自3.0以来DB名称有完全不同的命名约定，我们需要仔细区分db和DB的名称（旧版本与新版本）。

Here is what I've done to retain data: Since 3.0 has completely different naming conventions for DB names, we need to carefully distinguish db from both(Older vs newer).

对于2.X，Cassandra dbname的每个名称都有以下约定ks：

For 2.X Cassandra dbnames have the following convention for each ks:

keyspace-ColumnFamilyName-ka-ID-Data.db
keyspace-ColumnFamilyName-ka-ID-Digest.sha1
keyspace-ColumnFamilyName-ka-ID-Filter.db
keyspace-ColumnFamilyName-ka-ID-Index.db
keyspace-ColumnFamilyName-ka-ID-Statistics.db
keyspace-ColumnFamilyName-ka-ID-Summary.db
keyspace-ColumnFamilyName-ka-ID-TOC.txt

keyspace: keyspace name
ColumnFimilyname : Name of the CF under keyspace
ka: C* Internal(Haven't explored much on this)
ID: It is incremental value I see different sets of these having different id.(looks like it is an increasing factor  when it takes snapshot, not sure though)
And the last parameter is db name

因此，当我从2.1.7开始时，我会仔细阅读C中的每个日志语句*守护程序，发现系统键空间下的sstable_actiivity文件不是实际的文件，因为此文件的大小非常小。

So when I start with 2.1.7 I read through each and every log statement in of C* daemon and found out that the sstable_actiivity file under system keyspace is not the actual one as the size of this file is very less.

/data/system/sstable_activity-5a1ff267ace03f128563cfae6103c65e/system-sstable_activity-ka-145

所以我试图从快照中找到系统（键空间目录，即/ data / system /）下的最旧文件，并将其替换为上述文件。
和我在系统键空间下的 schema_keyspaces表中重复的操作。

So I tried to find the oldest file under system(keyspace directory i.e /data/system/) from snapshots and replace that with the above file. And the same I repeated for the "schema_keyspaces" table under system keyspace.

现在，我再次重新启动cassandra守护程序，幸运的是，我可以得到键空间列表运行 DESC密钥空间
但我对密钥空间执行 DESC TABLES 时看不到表列表，因为由于文件而未加载

Now I restart cassandra daemon again, luckily I could get list of keyspaces after I run "DESC KEYSPACES" But I don't see list of tables when I execute "DESC TABLES" for my keyspace as it didn't load because files were not found by sstable_activity.

现在，我一直对系统键空间下的所有其他表重复相同的过程。

Now I kept repeating the same process for all other tables under "system" keyspace. which are as below:

schema_keyspaces
schema_columnfamilies
local
schema_columns
schema_triggers
schema_usertypes

重启Cassandra之后，我能够检索到我的应用程序期望的日期。

After restarting Cassandra, I was able retrieve date that I expected for my application.

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