Postgresql – pgAdmin 4 Not connected to the server

pgadmin-4postgresql

I've installed Postgresql 11 and pgAdmin4 (version 4.5) and while I'm able to create tables in a new database, if I attempt to SELECT or INSERT into those tables I always get a message 'Not connected to the server or the connection to the server has been closed.' in the "Messages" tab in pgAdmin 4.

If, however, I open the SQL Shell I can execute a SELECT on a table that I've attempted to insert into from pgAdmin and it shows that the rows have been inserted.

Best Answer

I have exactly the same problem with 4.5 & 4.6. Postgres 10 server on Ubuntu, PG Admin on Windows 7. I downgraded PG Admin to 4.3 and it works.

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Postgresql – the sense to use server_lifetime with PgBouncer

This is base of pgBoouncer or any pooler software - the main work of pgBouncer is reusing PostgreSQL connections. Creating lot of connections can be very expensive for short sessions - with fast queries. When physical connection can be shared (reused) for more clients, you can get much faster execution.

Second important role of pgbouncer and similar software is a protection against overloading. PostgreSQL has not internal pooling - any connected user can run any SQL. There are lot of applications with long idle connections. These applications requires high MAX_CONNECTION number. Hidden assumption is low activity on these connections. But sometimes can be pretty high activity, pretty high requests on new connects and the database can be overloaded. The MAX_CONNECTION should be about 10 x CPU cores. Inadequate value doesn't protect database against overloading and finish by failure. For these application can be pgbouncer safe solution - this software is able to share physical idle connections for lot of clients.

The server_lifetime enforces returning allocated sources to operation system. Some sources (like memory) is internally managed and it is newer returned to operation system (usually). Some memory expensive operations can require lot of memory. First time this memory is allocated from system. Next times this memory is managed by PostgreSQL only - it is much cheaper and faster. But sometimes it can be ineffective too. pgbouncer has not information which process has preallocated memory - and sometimes memory can be used better. The safeguard is server_lifetime. One hour is conservative value - and can be shorter - 10 minutes. pgbouncer close only not active connection - so if the connection is used by any client: opened transaction, long active command, .. server_lifetime cannot be applied.

Postgresql – How to restart server without rebooting system

On CentOS server, you can use these below commands:

PostgreSQL 9.6:

/bin/systemctl restart postgresql-9.6.service

PostgreSQL 10.x

/bin/systemctl restart postgresql-10.service

PostgreSQL 11.x

/bin/systemctl restart postgresql-11.service

Best Answer

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Postgresql – the sense to use server_lifetime with PgBouncer

Postgresql – How to restart server without rebooting system

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