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PG when doing a clean shutdown calls postmaster to cleanly stop everything.
This means postmaster might take the checkpoint, archive and upload WAL files etc.
This can be a time consuming job. I want to know if there is a way to see how many (or size of) WAL files need to archived before sending the kill command to PG.
Is there a way to know/predict the time taken by PG stop by querying some pg tables?
Archiving is not your problem here, because WAL segments are filled one after the other and archived right when they are full. Also, there is no spike in WAL activity during a shutdown. There is only one final WAL segment that gets archived once the shutdown checkpoint is done.
What can take some time is the checkpoint that is executed during shutdown. There is a trick to speed that up: run an explicit checkpoint right before shutdown. Then the final checkpoint will have little to do and can finish quickly:
# explicit checkpoint to speed up the shutdown
psql -c CHECKPOINT
# shutdown the PostgreSQL server
pg_ctl stop
Related
I have installed postgresql on windows 10 on usb disk.
Every day when i start my pc in work from sleep and plug in the disk again then trying to start postgresql i get this error:
FATAL: the database system is starting up
The service starts with following command:
E:\PostgresSql\pg96\pgservice.exe "//RS//PostgreSQL 9.6 Server"
It is the default one.
logs from E:\PostgresSql\data\logs\pg96
2019-02-28 10:30:36 CET [21788]: [1-1] user=postgres,db=postgres,app=[unknown],client=::1 FATAL: the database system is starting up
2019-02-28 10:31:08 CET [9796]: [1-1] user=postgres,db=postgres,app=[unknown],client=::1 FATAL: the database system is starting up
I want this start up to happen faster.
When you commit data to a Postgres database, the only thing which is immediately saved to disk is the write-ahead log. The actual table changes are only applied to the in-memory buffers, and won't be permanently saved to disk until the next checkpoint.
If the server is stopped abruptly, or if it suddenly loses access to the file system, then everything in memory is lost, and the next time you start it up, it needs to resort to replaying the log in order to get the tables back to the correct state (which can take quite a while, depending on how much has happened since the last checkpoint). And until it's finished, any attempt to use the server will result in FATAL: the database system is starting up.
If you make sure you shut the server down cleanly before unplugging the disk - giving it a chance to set a checkpoint and flush all of its buffers - then it should be able to start up again more or less immediately.
I have this issue that is driving me nuts. Despite all my efforts, I am not able to force my postgres server to shut down. I have followed those instructions : http://www.question-defense.com/2008/10/17/pg_ctl-server-does-not-shut-down-force-postgres-to-shutdown
but still, nothing happens and all I got in the shell is
waiting for server to shut down............................................................... failed
pg_ctl: server does not shut down
Any help much appreciated.
Update: Checking the logs, I have this recurring error :
LOG: checkpoints are occurring too frequently (25 seconds apart)
HINT: Consider increasing the configuration parameter "checkpoint_segments".
After giving it a lot of thoughts especially on the way I installed it at the first place, I realize that I set up the install so the daemon would launch postgres at the start of my machine. Thus, any manual killing would simply result in the recreation of those process by the same daemon.
To resolve this problem you need to stop the daemon from working using launchctl and remove a .plist file in your postgres directory.
Good luck if you face the same problem.
You probably run with the default setting of "checkpoint_segments = 3", that produces the warnings. Your database does many writes, right? It takes some time to write all of this to disk, and your database is quite busy rotating the logfiles, instead doing real work.
If you increase checkpint_segments, you will see performance improvements, and less I/O.
For further readings: https://wiki.postgresql.org/wiki/Tuning_Your_PostgreSQL_Server
I am performing a bulk copy into postgres with about 80GB of data.
\copy my_table FROM '/path/csv_file.csv' csv DELIMITER ','
Before the transaction is committed I get the following error.
Server closed the connection unexpectedly
This probably means the server terminated abnormally
before or while processing the request.
In the PostgreSQL logs:
LOG:server process (PID 21122) was terminated by signal 9: Killed
LOG:terminating any other active server processes
WARNING:terminating connection because of crash of another server process
DETAIL:The postmaster has commanded this server process to roll back the current transaction and exit, because another server process exited abnormally and possibly corrupted shared memory.
HINT: In a moment you should be able to reconnect to the database and repeat your command.
Your backend process receiving a signal 9 (SIGKILL). This can happen if:
Somebody sends a kill -9 manually;
A cron job is set up to send kill -9 under some circumstances (very unsafe, do not do this); or
the Linux out-of-memory (OOM) killer triggers and terminates the process.
In the latter case you will see reports of OOM killer activity in the kernel's dmesg output. I expect this is what you'll see in your case.
PostgreSQL servers should be configured without virtual memory overcommit so that the OOM killer does not run and PostgreSQL can handle out-of-memory conditions its self. See the PostgreSQL documentation on Linux memory overcommit.
The separate question "why is this using so much memory" remains. Answering that requires more knowledge of your setup: how much RAM the server has, how much of it is free, what your work_mem and maintenance_work_mem settings are, etc. It isn't a very interesting problem to look into until you upgrade to the current PostgreSQL 8.4 patch release to make sure the problem isn't one that's already fixed.
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I think someone has already suggested:
1. stop the mongod
2. backup the data directory
Is it reliable, I mean, ensure 100% success to restore?
And I can't find which directory stores the data... any command can help me to find it?
If mongod process exits cleanly (that is, no crashes or kill -9 stuff), then it is safe to copy data files somewhere.
If your current installation breaks (for example, data corruption due to unclean shutdown), you can delete its files, copy that backup over and start mongod again.
Default data directory is /data/db, but it may be set to another value in your config file. For example, I set it to /var/lib/mongodb.
You can also use mongodump to do a backup from a live server (this may impact performance). Use mongorestore to restore backups made by mongodump.
At IGN we do hot backups via mongodump running as an hourly cron job, and take filer snapshots (NetApp storage) on a half-hourly basis. If your system is not too write heavy and you can afford write blocks, try using fsync and lock to flush the writes to the disk and prevent further writes. This can be followed by mongodump and upon completion you can unlock the db. Please note that you've to be admin to do so.
db.runCommand({fsync:1,lock:1})
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.