Heikki Linnakangas wrote:
Florian G. Pflug wrote:
Jeff Davis wrote:
Are you referring to the size of the xip array being a problem? Would it
help to tie the size of the xip array to max_connections? I understand
that max_connections might be greater on the master, but maybe something

Thats what I currently do - the xip array on the slave is sized to
hold max_connections entries (Actually, it's max_connections +
max_prepared_xacts I think). The problem occurs exactly if those
values are set too small on the slave - and since shared mem
objects are not resizeable, I don't see how the slave can handle
an xip overflow gracefully other than by not publishing the
information in shared memory as long as it doesn't fit there.

You could store the value of max_connections in the checkpoint xlog record, and read it from there in the slave. Though one could still change it on the master and restart without restarting the slave as well.

But AFAIK shmem allocation happens before recovery starts... Even if this
was solved, it would only be a partial solution since as you note, the
master might be restarted while the slave keeps running. So I think it's
better not too add too much complexity, and just tell the DBA to increase
max_connections on the slave, together with a comment in the documentation
never to sex max_connections smaller on the slave than on the master.

greetings, Florian Pflug

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