I am working as a Postgres DBA at my organization. We are currently working on Postgres 9.5 on SUSE Linux servers. I wanted a specific solution. We have multiple SUSE Linux servers and each server can host one or more Postgres database. My requirement is I need to find the list of all the database available on a particular server irrespective of the database is up and running or its shut down.
Is there any file or any location where Postgres keeps note of all the databases that is created on a server. Is there a way I can get the required details without connecting to the Postgres instance and without running any PSQL commands?
If not what would be the best way to get the list. Any hints, solutions and thoughts would help me to resolve this issue.
Thanks a lot for the help in advance.
In PostgreSQL, a server process serves a database cluster, which physically resides in a data directory.
A PostgreSQL cluster contains several databases, all of which are shut down when the server process is shut down.
So your question can be split into two parts:
How to find out which database clusters are on a machine, regardless if they are started or not?
How to find out all databases inside a cluster even if the cluster is shut down?
There is no generic answer to the first question, since a data directory could in principle be everywhere and could belong to any user.
You could get an approximation with
find / -name PG_VERSION
but it is probably better to find a special solution that fits your setup (about which you didn't tell us).
The second question is even harder.
To even get a list of numeric IDs, you would have to know all tablespace directories. Those in the default tablespace are the names of the subdirectories in the base subdirectory of the data directory.
In order to get the names of the databases you have to have the PostgreSQL server started, because it would be very hard to find the file that belongs to pg_database and parse it.
Related
Here is the background:
I am currently running an ETL process on a linux server (CentOS 8) which also hosts applications which read from a local SQLite database.
At certain times when the ETL is running and writing to the SQLite database, applications are also reading from the database.
In order to avoid database locking when the SQLite database is in use by the applications, I have enabled WAL on the SQLite database so that the ETL may write to the database while applications are in use.
However there is now the following issue whereby the ETL process is unable to query the database after the connection has been established. I have logged the following information when this occurs:
The 'shinysuite' user runs the ETL process.
The 'shiny' user runs the applications.
According to the admin, these users belong to the same group.
Output from /etc/groups
First, I do not understand why the 'shiny' user owns the -wal file even though it only reads.
Second, I do not understand why the ETL process ('shinysuite') would be unable to read from the -wal file even it did not own the file.
What could be the problem here?
First, I do not understand why the 'shiny' user owns the -wal file even though it only reads.
When reading from a WAL-mode sqlite3 database, the helper -wal and -shm files are created if they don't already exist.
They're owned by the shiny user and belong to the shiny group, but shinysuite is not a member of that group so it doesn't have permission to use the files. If your application being run by shiny does so in the shinysuite group instead of shiny (If it's a binary executable, using chgrp(1) to change the group of the file and then making it set-gid with chmod g+s shinyapp is one way, or maybe just add shinysuite to the shiny group.) it should work.
when i create a postgresql database and create tables and columns and even insert data into the columns. I cant restart my machine without losing the created databases and all the data.
i have tried changing a coupe things in the configuration file but nothing helped.
I also have to reset the password for postgres everytime I restart my machine. I mainly use mongodb I am just learning postgreSQL just so I can use it if I ever need to in the future. I am runing a Linux machine QubesOS. I have a few problems like this useing QubesOS. every tutorial I watch everybody uses Macs. Which a mac seems good and all kinda a mix between windows and linux The best of both worlds. Easy package installs and terminal control but I dont want to trade my linux machine for a Mac I would much rather just fix these problems I am having with PostgreSQL on my linux machine
You ran into an important security feature of QubesOS: All data modifications are discarded on shutdown of a so called "Qube". They are reset to their original state.
But there is the exception of data kept in some very special directories.
If you convince your data base packages to put their data into these directories, it will be preserved over reboots of your data base Qube:
Read this documentation for more information.
I'm a newbie in MongoDB. And I'm sorry if the Question is not clear enough. What i mean is:
I have clustered GlusterFS Volumes (configured on top of 2 CentOS). Which means, same data directory can be read from both CentOS boxes:
Lets call: CentOS-1 and CentOS-2
And i wanna install MongoDB Servers mongod on both CentOS boxes. But start (run) only one. (The other one on CentOS-2 might be purposely stopped)
Then the Applications will be connecting to that one (current Active) on CentOS-1.
Here the main question comes in (please refer to the picture below):
Let's say: if CentOS-1 Server goes down, and i manually start the another MongoDB Server (mongod on the another box CentOS-2), and let all the Applications to connect to CentOS-2:
(1) Will everything be still working?
(2) Will there be 'lock' issues as in MySQL?
(3) If it works, does it mean, we can add any amount of MongoDB Servers (in stand-by mode), and whenever they swing, there's no problem?
Note:
Only 1 Server at a time will be running. Not like: the Data Store is being accessed by multiple Server.
Thanks for all opinions in advanced :)
Yes you can. There won't be any problem in moving the data files to a different server as long as you plan to use the same version of mongodb and the same operating system. When you move the files make sure to delete the mongodb.lock file if it exists in data directory.
Glusterfs is good for file replication between various servers, but its not good idea to sync mongodb data using glusterfs.
Will everything be still working?
probabily no
Will there be 'lock' issues as in MySQL?
yes it will be. check this https://docs.mongodb.org/v3.0/faq/concurrency/ .glusterfs locks the file while it write on gluster-volumes and mongodb data may change frequently which could result problem.
you can consider mongodb replication (https://docs.mongodb.org/manual/core/replication-introduction/) for your purpose
Our company has an old linux server that runs a few tomcat web applications. One of those applications is connecting to PostgreSQL. While I'm a C#.Net/Windows coder, I need to connect to this database from my computer using pGAdmin III (or any suggested equivalent). When attempting the connection, pgAdmin says Server Not Listening.
Without knowing much about linux I'm using WinSCP to connect to the file structure. I have ZERO documentation on the old apps, any data sources, or their data connections. I've been able to determine the following, assuming the location of the web app is actuallly legit and not some non-running copy.
PostgreSQL
In one app's connection information:
jdbc:postgresql://localhost:5432/somename
After some digging, I found the following possible instances of postgresql on the server file structure.
\etc\postgresql\8.3\main
\etc\postgresql\8.4\main
There's also \etc\postgresql-common with very different types of files in there.
If there are other instances or related folder, I am unaware and wouldn't know where to look. It's a labyrinthine beast.
I ensured in the config file for both that listening="*", which was supposed to be one of two fixes. It was already set to *, so assuming one of these is the right one, I should be good there.
I know that at least some instance of postgresql is turned on because the old app is running and fetching data, so that's the other of the two fixes.
pgAdmin
I heard in a separate thread here that reinstalling pgAdmin might solve the problem, but it did not. I tried with and without ssl.
Here is how I'm trying to set up the connection in pgAdmin III:
Name: SomeName
Host: I've tried a few combinations here. //servername/somename, or just //servername
Port: 5432 (matches what was expected, also the port from the connection)
Service: Blank
MaintenanceDB: I tried the default in pgadmin, postgres and the actual db I'm trying to connect to.
username & Password: the credentials from the connection info in the old app.
I'm getting the Server Doesn't Listen, suggesting that either it's not on (Well...some data source is on and working and the data in WEB-INF suggests it's postgresql), or it's not accepting TCP/IP connections, which it is according to the instances of postgresql I was able to find.
Long Story Short
At this point I'm assuming that one of the following is the problem...
The connection information I'm entering into postgreSQL is not being entered correctly, but I don't know what I'm doing wrong.
The source of the connection information (the web application) is bad/old/not from a running instance (and in this case I don't know how to tell, not in linux).
The instances of postgresql I found are not the instances it's using, and I have no idea how to find it.
Something's fishy network-wise, but since both my computer and the linux server are on the same network, it doesn't seem too likely.
Also, everyone, please document your stuff for the poor souls of the future. I greatly appreciate any assistance you are able to offer me.
You may want to use a tunnel:
ssh -L 5432:localhost:5432 user#server
After you log into the remote server, you'll have mapped port 5432 on your computer to the remote one. Then you can use pgAdmin to connect to your localhost on port 5432. Make sure you don't have anything running on this port on your computer.
Edit: Look at these examples on how to setup tunnels using putty
We have a linux server for the database. Most of our data are on /var/. I would like to backup entire directory on external hard drive or on another linux system so that if something goes wrong I can entirely replace the directory. Since the directory has many files, I do not want to copy and paste every time instead I like to sync them.
Is there easy way to do that? rsyn can do that, how do I avoid of login every time the server? BTW I have limited knowledge of linux system.
Appreciated any comments and suggestions.
Bikesh
Rsyncing database files is not a recommended way of backing them up. I believe you have mysql running on the server. In that case, you can take a full database dump in the server, using steps mentioned in following link:
http://www.microhowto.info/howto/dump_a_complete_mysql_database_as_sql.html#idp134080
And, then syncing these files to your backup server. You can use rsych command for this purpose:
http://www.tecmint.com/rsync-local-remote-file-synchronization-commands/
Make sure that you have installed mysql in the backup server too. You can also copy the mysql configuration file /etc/my.cnf file to the database backup server. In case you require your database to be updated always, you can setup mysql replication. You can follow the below mentioned guide to do the same.
http://kbforlinux.blogspot.in/2011/09/setup-mysql-master-slave-replication.html