[GitHub] [arrow-adbc] zeroshade commented on issue #64: [Format] Formalize thread safety and concurrency guarantees

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zeroshade commented on issue #64:
URL: https://github.com/apache/arrow-adbc/issues/64#issuecomment-1215277102

   > An individual statement can be used multiple times, but result sets cannot be read concurrently (that is: executing a statement invalidates prior result sets)
   
   Are we referring to result sets from *different queries* or only putting a limitation on result sets from a single prepared statement? Go's Query returns a `Rows` object which is then used to iterate over the results, but there's no requirement on *when* that iteration can happen. To guarantee safety we'd have to buffer the entire result set into memory to ensure that they don't get invalidated by a subsequent query, which would be extremely undesireable. This would also technically be true for the proposed ADBC API which just populates the `ArrowArrayStream*` and let's the consumer decide how/when to iterate that stream and release it. This seems like an extraordinarily painful requirement.
   
   > Prepared statements follow regular statements in behavior. (This makes Golang support a little weird; Golang is exceptional in allowing concurrent use of prepared statements)
   
   So I looked at the docs again, and as per my comment [here](https://github.com/apache/arrow-adbc/issues/64#issuecomment-1214417469) I was wrong. While the prepared statement can be used by multiple goroutines, it will not be used concurrently by those goroutines. Basically the `database/sql` package's `sql.Stmt` object is safe for concurrent use, but it internally ensures serialization to it's calls to the underlying Driver's `driver.Stmt` object. It is, however, bound to a single Connection object. 


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