rabbit_db_exchange: Always use a transaction to bump exchange serials (backport #15236)#15238
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rabbit_db_exchange: Always use a transaction to bump exchange serials (backport #15236)#15238
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[Why] Initially, I thought a transaction would be too much for a simple counter. Therefore I use a regular `get`, plus a `put` with a condition on the tree node payload version to ensure the put would only succeed of the read value was still the one in the store. Unfortunately this technic is very inefficient with a lot of concurrency. That's because all processes will read the same value and will all commit a `put`, but only one of them will succeed. After that, all but on will retry the same read/modify/write with the same poor result. In the end, all processes are spamming `put` commands and they make very little progress, loading the store in the process. [How] This patch goes back to a simple transaction. This solves the contention issue. (cherry picked from commit 66abb3a)
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Why
Initially, I thought a transaction would be too much for a simple counter. Therefore I use a regular
get, plus aputwith a condition on the tree node payload version to ensure the put would only succeed of the read value was still the one in the store.Unfortunately this technic is very inefficient with a lot of concurrency. That's because all processes will read the same value and will all commit a
put, but only one of them will succeed. After that, all but on will retry the same read/modify/write with the same poor result. In the end, all processes are spammingputcommands and they make very little progress, loading the store in the process.How
This patch goes back to a simple transaction. This solves the contention issue.
This is an automatic backport of pull request #15236 done by Mergify.