Overpass API developpement

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Hello,
I'm new to overpass. I've run into some issues and would appreciate any
pointers that might help resolve them.
I have set up a local overpass server.

1. For a particular query I have I see the following line in the
transactions.log
    'Oversized: runtime x seconds, size 541110848 bytes in line 1, statement
query

    From reading some of the docs and other user's experiences I was looking
to try the maxsize parameter with the query.

    However, when I run the same query -still without maxsize parameter-
against another instance of overpass, there is no such message and the server
responds to the query.

Both instances, have 8G RAM.
The differences between the two instances are:

a. Server with error in transactions log is dispatcher version 0.7.55.6
    Server without error in transactions log is dispatcher version 0.7.55.7

b. Server with error in transactions log is the planet database
    Server without error is a local region.
    The query is identical to both servers.

-->Any insight into why the one machine errors out?

2. The available free RAM is just above 7G at the time of the query resulting
in an error. I was running minute updates. I disabled minute updates but the
error didn't resolve. There is no other activity on the machine.  I started
the server using the default 12G maxsize.

-->Why doesn't/didn't overpass allocate the available RAM

Thank you