I'm having a remote machine that's using postgresql 9.2.1. Suddenly, i couldn't start my pgsql server(pg_isready command is rejecting connections). what my doubt is that, is there any possibility that i can start my database in Standalone back end mode, while it is not opening in Normal user mode?
And, what is the difference in starting the pgsql server in those two modes?
Thanks in advance.
Rather than using single user mode, look into the PostgreSQL server log file. That should tell you what the problem is.
In single-user mode, there will be just a single process accessing the database; none of the background processes are started. You'll be superuser, and the database process will last only for the duration of your session. This is something for emergency recovery, like when system tables are corrupted, you forgot your superuser password and so on.
In your case, single-user mode will probably only help if the database shut down because of an impending transaction ID wraparound. You can then issue the saving VACUUM (FREEZE) in single-user mode.
As soon as you have fixed your problem, upgrade to a supported release of PostgreSQL.
Related
I have inherited a PostgreSQL 13 cluster which was setup using log shipping. I had to make a few changes and would to confirm everything is working well.
Is there a command to make pgsql report whether it is in standby mode or active mode?
Is there a command to make pgsql report up to which WAL file it has applied changes?
I assume that the only way to test the wal shipping is working is to manually modify the active db server and watch for the change on the standby?
I know there are better ways to setup a cluster, but for now I just need to ensure the system remains operational as setup.
From the doc:
select pg_is_in_recovery();
select pg_walfile_name(pg_last_wal_replay_lsn());
Either that or select pg_current_wal_lsn(); on the primary, then select pg_wal_lsn_diff(pg_current_wal_lsn__taken_from_primary,pg_last_wal_replay_lsn()); on standby as commented by #Laurenz Albe.
Original aim: rename a database using ALTER DATABASE via psql.
Problem: rename fails due to other sessions accessing target database. ・All terminals/applications I am aware of have been closed.
・querying pg_stat_activity shows that there are 10 processes(=sessions?) accessing the db.・The username for each session is the same user I have been using for psql and for some local phoenix and django apps. The client_addr is also local host for all of them.
・When I use pg_terminate_backend, on any of the pids, another process gets immediately spawned.
・After restarting my pc, 10 processes are again spawned.
Concern: As I can't account for these 10 processes that I can't get rid of, I think I'm misunderstanding how postgres works somewhere.
Question: Why do 10 session/processes connected to a particular one of my databases, and why can't I terminate them using pg_terminate_backend?
Note: In the phoenix project I set up recently, I set the and set the pool_size of the Repo config to 10 - which makes me think it's related...but I'm pretty sure that project isn't running in any way.
Update - Solved
As a_horse_with_no_name suggested, the by doing the following I was able to put a stop to the 10 mystery sessions.
(1) prevent login of user responsible for the sessions (identifiable by querying `pg_stat_activity`), by doing `alter user .... with nologin`
(2)-running pg_terminate_backend on each of the session's pids.
After those steps I was able to change the table name.
The remaining puzzle is, how did those sessions get in that status in the first place... from the contents of pg_stat_activity, the wait_event value for each was clientRead.
From this post, it seems that the application may have been forcibly stopped halfway through a transaction or something, leaving postgres hanging.
A slave database was set up some time ago for the purpose of backing up or replicating a remote database. However I can no longer write to the database using a Delphi based ETL (the ETL works for another database pair, but to date has never been used for this particular pair). The replication database was setup by somebody else who has since left the company. I am reasonably sure this has been setup as a replication database, however the employee who has since left told me that replication never worked for unrelated reasons. Using the ETL we can (using SQL queries) read from the one database, and write back to the replication database, Or should be able to, as it is currently read only.
I have tried:
Maintenance such as VACUUM
Attempt to drop tables and the entire database
Restore a full backup from the master database
None of these work, and I am told the database is read-only.
I have looked at postgresql.conf and see that hot_standby is checked, so I think (but am not 100% certain) that the database is in some sort of replication mode (I've never touched replication as supported by Postgres, so I wouldn't know).
I have checked permissions in pg_hba.conf and see there are some credentials in there for replication. I am not sure whether this activates "replication mode" for the database, or simply means these credentials are for replication only.
I have been through months worth of log files (This has not been working since our IT department upgraded the entire network about 5 months ago). I see the log file contents seen below, repeated over and over with nothing else for months. Note the IP address shown below is listed in the pg_hba.conf file, so credentials are valid.
The database is in recovery mode, as I have found by using:
select pg_is_in_recovery();
This explains to me why it's read only, but why can I not restore databases, or just simply dump the entire database and start again (it's a backup so losing/restoring it is not an issue)?
I was tempted to try modifying the recovery.conf file (which exists) but I read/believe that once recovery has been initiated (which in my case it has) modifying the file will have no effect.
I'm using a legacy version of Postgres: 9.2.9
Any help here would be greatly appreciated, as I have been working solidly on this for more than a day now.
Log File entry (sample):
FATAL: could not connect to the primary server:
FATAL: no pg_hba.conf entry for replication connection from host "192.168.20.2", user "postgres", SSL off
FATAL: could not connect to the primary server: server closed the connection unexpectedly
This probably means the server terminated abnormally before or while processing the request.
A couple of options would work for me:
Convert the database from being a read-only replication database, to a standard read/write database or
Dump/drop the entire database so I can create a new one with write capabilities.
It looks like the two database clusters have been set up for replication, but configuration changes on one of the machines broke the replication (changed pg_hba.conf on the primary, changed IP addresses, …).
Here is the way to your desired solutions:
Bringing the standby out of recovery mode: Run
/path/to/pg_ctl promote -D /path/to/data/directory
on the standby as operating system user postgres.
Nuking the standby: Remove the data directory on the standby with rm -rf (or the equivalent on your operating system). Kill all PostgreSQL processes.
Then use initdb to create a new database cluster in the same location.
I have dozens of unlogged tables, and doc says that an unlogged table is automatically truncated after a crash or unclean shutdown.
Based on that, I need to check some tables after database starts to see if they are "empty" and do something about it.
So in short words, I need to execute a procedure, right after database is started.
How the best way to do it?
PS: I'm running Postgres 9.1 on Ubuntu 12.04 server.
There is no such feature available (at time of writing, latest version was PostgreSQL 9.2). Your only options are:
Start a script from the PostgreSQL init script that polls the database and when the DB is ready locks the tables and populates them;
Modify the startup script to use pg_ctl start -w and invoke your script as soon as pg_ctl returns; this has the same race condition but avoids the need to poll.
Teach your application to run a test whenever it opens a new pooled connection to detect this condition, lock the tables, and populate them; or
Don't use unlogged tables for this task if your application can't cope with them being empty when it opens a new connection
There's been discussion of connect-time hooks on pgsql-hackers but no viable implementation has been posted and merged.
It's possible you could do something like this with PostgreSQL bgworkers, but it'd be a LOT harder than simply polling the DB from a script.
Postgres now has pg_isready for determining if the database is ready.
https://www.postgresql.org/docs/11/app-pg-isready.html
What can be done to prevent having to restart a PC after a program (C++Builder) terminated abnormaly without closing the database using firebird 2?
What I am looking for: I would like to be able to just restart the program without any other intervention. (I could have the user call a batch file executing some cleanup or add some lines of code to the program to disconnect everything.)
If your database is firebird 2.1+, there are monitoring tables that show the active connections, and the sysdba can manually delete any left-over connnections.
If you look in your release notes, the syntax details should be there.