What is the expected behavior for postgresql processes when system time is changed?
For eg: A case is seen with postgres autovacuum process that, it is not working after time has been changed and only solution is to restart the Database.
Related
I am using physical replication with 1 standby in postgres v.14.4. The max_standby_archive_delay and max_standby_streaming_delay parameters are configured by default at 30s. if a pg_dump is executed on the standby side will the snapshot taken during data export be consistent despite small values for these parameters.
The pg_dump will be consistent, but obviously not at exactly the same point in time as one run simultaneously on your primary.
Note that longer-running transactions can be aborted on the standby if your replication configuration is set up to do so.
Clarification: Yes, of course the dump as a whole will be consistent - it would be useless otherwise. The program executes all its queries in a single snapshot. If you run it a second time, the second snapshot will be different from the first, but each dump will be internally consistent.
What actually Happend:
Running windows 7 on my system and system was shutdown due to power failure. when system restarted, I opened PostgreSQL and all my databases were deleted.
I checked logs and there were some entries
Database system was intrupted ; last known up at (dateTime)
Database system was not properly shutdown; automatic recovery in progress
Record with zero length at 0/C9B92168
Redo is not required
Can anybody tell me how can i recover my databases, as I don't have restore point.
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.
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
My company's website uses a PostgreSQL database. In our data center we have a master DB and a few read-only slave DB's, and we use Londiste for continuous replication between them.
I would like to setup another read-only slave DB for reporting purposes, and I'd like this slave to be in a remote location (outside the data center). This slave doesn't need to be 100% up-to-date. If it's up to 24 hours old, that's fine. Also, I'd like to minimize the load I'm putting on the master DB. Since our master DB is busy during the day and idle at night, I figure a good idea (if possible) is to get the reporting slave caught up once each night.
I'm thinking about using log shipping for this, as described on
http://www.postgresql.org/docs/8.4/static/continuous-archiving.html
My plan is:
Setup WAL archiving on the master DB
Produce a full DB snapshot and copy it to the remote location
Restore the DB and get it caught up
Go into steady state where:
DAYTIME -- the DB falls behind but people can query it
NIGHT -- I copy over the day's worth of WAL files and get the DB caught up
Note: the key here is that I only need to copy a full DB snapshot one time. Thereafter I should only have to copy a day's worth of WAL files in order to get the remote slave caught up again.
Since I haven't done log-shipping before I'd like some feedback / advice.
Will this work? Does PostgreSQL support this kind of repeated recovery?
Do you have other suggestions for how to set up a remote semi-fresh read-only slave?
thanks!
--S
Your plan should work.
As Charles says, warm standby is another possible solution. It's supported since 8.2 and has relatively low performance impact on the primary server.
Warm Standby is documented in the Manual: PostgreSQL 8.4 Warm Standby
The short procedure for configuring a
standby server is as follows. For full
details of each step, refer to
previous sections as noted.
Set up primary and standby systems as near identically as possible,
including two identical copies of
PostgreSQL at the same release level.
Set up continuous archiving from the primary to a WAL archive located
in a directory on the standby server.
Ensure that archive_mode,
archive_command and archive_timeout
are set appropriately on the primary
(see Section 24.3.1).
Make a base backup of the primary server (see Section 24.3.2), and load
this data onto the standby.
Begin recovery on the standby server from the local WAL archive,
using a recovery.conf that specifies a
restore_command that waits as
described previously (see Section
24.3.3).
To achieve only nightly syncs, your archive_command should exit with a non-zero exit status during daytime.
Additional Informations:
Postgres Wiki about Warm Standby
Blog Post Warm Standby Setup
9.0's built-in WAL streaming replication is designed to accomplish something that should meet your goals -- a warm or hot standby that can accept read-only queries. Have you considered using it, or are you stuck on 8.4 for now?
(Also, the upcoming 9.1 release is expected to include an updated/rewritten version of pg_basebackup, a tool for creating the initial backup point for a fresh slave.)
Update: PostgreSQL 9.1 will include the ability to pause and resume streaming replication with a simple function call on the slave.