Avoid LMDB exception during recursive lookup #15090
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The check was too strict and would prevent any RO transaction to coexist with RW transactions. But LMDB is designed to allow this - on the other hand there can be only one active RW transaction at a time.
miodvallat
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Short description
It has been noticed that using
includestatements in Lua records served by LMDB would cause aSERVFAILresult, with aDuplicate RW transactionexception report in the server logs.This is caused by almost all LMDB transactions in the server being considered as RW transactions, even when they aren't; LMDB does not allow for more than one writer to operate at the same time, by design.This PR reworks the way the RO/RW status of the transaction is decided, and correctly uses RO transactions. Note that the existing lmdb access code here seems to be written assuming an LMDB RW transaction is not allowed to coexist with any other transaction, even RO ones. If I am wrong on this, I have a much simpler fix (one-liner) to propose instead.Edit: these changes introduced a chicken-and-egg problem, as they would not allow new databases to be created. Oops. So I am pushing the one-liner fix I mentioned instead, and crossing fingers.
Checklist
I have: