Releases the prepared statements queued for release.
Removes a prepared statement from the list of statements to be released from the server. Does nothing if the statement isn't on the list.
Ids of prepared statements to be released. This uses assumeSafeAppend. Do not save copies of it.
Keeps track of prepared statements queued to be released from the server.
Prepared statements aren't released immediately, because that involves sending a command to the server even though there might be results pending. (Can't send a command while results are pending.)