I'm on RHEL6 and have installed PostgreSQL. Now whenever I want to start development I need to run the following command to start PostgreSQL
/opt/PostgreSQL/9.5/bin/postgres -D /opt/PostgreSQL/9.5/data
Then it halts for that terminal and I need to start another session of postgresql into another terminal. Whats wrong in Installation? and How to rectify this problem?
Image of practical for better understanding
https://www.postgresql.org/docs/current/static/app-postgres.html
The utility command pg_ctl can be used to start and shut down the
postgres server safely and comfortably.
If at all possible, do not use SIGKILL to kill the main postgres
server. Doing so will prevent postgres from freeing the system
resources (e.g., shared memory and semaphores) that it holds before
terminating. This might cause problems for starting a fresh postgres
run.
use pg_ctl -D /opt/PostgreSQL/9.5/data start instead, otherwise one day your database will tell you about corrupted data
Related
I am importing a large Postgresql dump file (2m+ rows) in Ubuntu (started the process via an Adminer "import") and am now regretting it as it is taking very long. It's the kind of dump file created by pg_dump that starts COPY table (columnd, column) FROM stdin. What is the safe way to kill this process now?
Regular kill is not doing anything. Nor is pg_cancel_backend. Tried sudo pkill -u postgres as well without success.
How can I stop this process now without crashing anything?
I am using helios Eclipse for debugging my code in postgresql.
My aim is to know how postgresql uses join algorithms during the join query, so I started to debug nodenestloop.c which is in the Executor folder.
I gave break points in that file, But whenever I try to debug that file, the control goes to main.c and never comes back,How do I constraint the control only to that particular file(nodenestloop.c)
Below are the following fields which I gave in Debug configurations of Helios Eclipse.
C/C++ Application - src/backend/postgres and
project - pgsql
I followed the steps given in the following link for running the program.
https://wiki.postgresql.org/wiki/Working_with_Eclipse#
I even uncheked the field "Start on Start up=main" , but When I do that, The step in and Step over buttons are not activated and the following problem has popped up.
Could not save master table to file '/home/ravi/workspace/.metadata/.plugins/org.eclipse.core.resources/.safetable/org.eclipse.core.resources'.
/home/ravi/workspace/.metadata/.plugins/org.eclipse.core.resources/.safetable/org.eclipse.core.resources (Permission denied)
So I started eclipse using sudo, but this time the following error has come in the console of eclipse.
"root" execution of the PostgreSQL server is not permitted.
The server must be started under an unprivileged user ID to prevent
possible system security compromise. See the documentation for
more information on how to properly start the server.
Could any one help me with this.
Thank you
Problem 1: User ID mismatch
Reading between the lines, it sounds like you're trying to debug a PostgreSQL instance that's running as the postgres user, or a different user ID to your own anyway. Hence your attempt to use sudo.
That's painful, especially when using an IDE like Eclipse. With plain gdb you can just sudo the gdb command to the desired uid, e.g. sudo -u postgres -p 12345 to attach to pid 12345 running as user postgres. This will not work with Eclipse. In fact, running it with sudo has probably left your workspace with some messed up file permissions; run:
sudo chown -R ravi /home/ravi/workspace/
to fix file ownership.
If you want to debug processes under other user IDs with Eclipse, you'll need to figure out how to make Eclipse run gdb with sudo. Do not just run all of Eclipse with sudo.
Problem 2: Trying to run PostgreSQL under the control of Eclipse
This:
"root" execution of the PostgreSQL server is not permitted. The server must be started under an unprivileged user ID to prevent possible system security compromise. See the documentation for more information on how to properly start the server.
suggests that you're also attempting to let Eclipse start postgres directly. That's very useful if you're trying to debug the postmaster, but since you're talking about the query planner it's clear you want to debug a particular backend. Launching the postmaster under Eclipse is useless for that, you'll be attached to the wrong process.
I think you probably need to read the documentation on PostgreSQL's internals:
Tour of PostgreSQL Internals
PostgreSQL internals through pictures
Documentation chapter - internals
Doing it right
Here's what you need to do - rough outline, since I've only used Eclipse for Java development and do my C development with vim and gdb:
Compile a debug build of PostgreSQL (compiled with ./configure --enable-debug and preferably also CFLAGS="-ggdb -Og -fno-omit-frame-pointer"). Specify a --prefix within your homedir, like --prefix=$HOME/postgres-debug
Put your debug build's bin directory first on your PATH, e.g. export PATH=$HOME/postgres-debug/bin:$PATH
initdb -U postgres -D $HOME/postgres-debug-data a new instance of PostgreSQL from your debug build
Start the new instance with PGPORT=5599 pg_ctl -D $HOME/postgres-debug-data -l $HOME/postgres-debug-data.log -w start
Connect with PGPORT=5599 psql postgres
Do whatever setup you need to do
Get the backend process ID with SELECT pg_backend_pid() in a psql session. Leave that session open; it's the one you'll be debugging.
Attach Eclipse's debugger to that process ID, using the Eclipse project that contains the PostgreSQL extension source code you're debugging. Make sure Eclipse is configured so it can find the PostgreSQL source code you compiled with too (no idea how to do that, see the manual).
Set any desired breakpoints and resume execution
In the psql session, do whatever you need to do to make your extension run and hit the breakpoint
When execution pauses at the breakpoint in Eclipse, debug as desired.
Basic misunderstandings?
Also, in case you're really confused about how all this works: PostgreSQL is a client/server application. If you are attempting to debug a client program that uses libpq or odbc, and expecting a breakpoint to trigger in some PostgreSQL backend extension code, that is not going to happen. The client application communicates with PostgreSQL over a TCP/IP socket. It's a separate program. gdb cannot set breakpoints in the PostgreSQL server when it's connected to the client, because they are separate programs. If you want to debug the server, you have to attach gdb to the server. PostgreSQL uses one process per connection, so you have to attach gdb to the correct server process. Which is why I said to use SELECT pg_backend_pid() above, and attach to the process ID.
See the internals documentation linked above, and:
PostgreSQL site - coding
PostgreSQL wiki - developer resources
Developer FAQ
Attaching gdb to a backend on linux/bsd/unix
I also faced similar issue and resolved it after some struggle
I misunderstood the following point under Debugging with child processes in the wiki (https://wiki.postgresql.org/wiki/Working_with_Eclipse).
5."Start postmaster & one instant of postgresql client (for creating one new postgres)"
The above step should be performed from terminal by starting postgres server and one client.
Hope this helps
Once this is done then debugger in eclipse needs to be started for C/C++ Attach to Application
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
I'm trying to install PostgreSQL on Cygwin as a user and i'm getting stuck on the part where I have to create a database server, after i execute the pg_ctl command, it just prints "server starting" and runs in the foregorund indefinitely, here's a picture of what I'm talking about:
http://postimg.org/image/oh7ucgt9h/
Im generally a beginner to databases so any pointers would be great.
Chances you are hanging allocating shared memory. Please go with the native Windows build instead. It is far easier to manage.
However if you insist, make sure the ipc-daemon is running before you run PostgreSQL. This will probably solve your problem.
You could run:
ipc-daemon --install-as-service
net start ipc-daemon
And this should do it.
I am trying to terminate a session (a specific session or all sessions, doesnt matter) in postgresql 8.3 and am having trouble doing that. I know in newer versions (8.4 and later) there is a pg_terminate_backend command that will do the trick but this is not available in postgresql 8.3. If I use pg_stat_activity, I can see all the sessions that are active but have no way of terminating them.
The solution does not have to necessarily be sql commands but I would like it to be independent of the OS that is being used (i.e. no DOS/UNIX commands).
Stopping and starting the postgres service in windows services works perfectly but this is an OS specific approach. Using 'pg_ctl restart -D DATA_DIR' does not stop the service however. Actually using pg_ctl to try and restart the service at the time I am trying to do it causes some weird behavior. If there is a way I can somehow use pg_ctl to force shutdown the process like I assume windows does, then I can probably use that.
Anyways, I am looking for a way to terminate one or all sessions in postgresql 8.3 that is not platform specific. Any help would be great!
You can use pg_cancel_backend():
select pg_cancel_backend(55555);
You can use this with pg_stat_activity. For example:
select pg_cancel_backend(procpid)
from pg_stat_activity where current_query='<IDLE>';
If that doesn't work you can try this:
pg_ctl kill -TERM pid
That should be OS independent. I'm not sure if there's any real difference in behaviour.
Other than that you could try stopping and starting the server, but you indicated odd behaviour from that. (What kind?)
Finally, for an OS specific option, on linux you can of course try using the kill command. kill -15 (SIGTERM) is safe; that's basically what pg_terminate_backend uses: kill -15 <pid>. kill -9 is moderately unsafe and you should use it only as a last resort.
su - posgres
psql
SELECT pg_terminate_backend(pg_stat_activity.procpid) FROM pg_stat_activity WHERE procpid <> pg_backend_pid() AND datname = 'dbname' ;
drop database "database name";