All of this I/O tend to happen in async thread, and typical deployments will have separate volumes for logs and data files, so we can parallelize everything instead of competing with one another.By the way, I’m running this series based on my own experience in building databases, and I’m trying to simplify it as much as it is possible to simplify such a complex topic.don’t want to ever need it, and you just throw it in the most efficient way to a drawer and will sort if out when you need to.Since we can match it up to the position of the data on the journal, we can safely say that the next time we recover, we can start reading the journal from that location.
Also check the DNS server -- if that's down then the copier can't resolve host names to IP addresses.
We can let the operating system handle all of that.
I mentioned that fsync is a pretty expensive operation to do.
But this is pretty much required if you need to get proper durability in the case of a power loss.
In most database engines that implement a journal, there is this distinction, the journal is strict for durability and recovery, and the data file(s) are used to actually store the data in order to operate.
If we had additional writes, from later in the journal file, that ended up physically in the data file, it doesn’t matter, because they will be overwritten by the journal entries that we have.
Doing it this way allows us to generate large batches of I/O, and in most cases, allow the operating system the freedom to flush things from the buffers on its own timeline, we just make sure that this doesn’t get into degenerate case (where we’ll need to read tens of GB of journal files) by forcing this every now and then, so recovery is fast in nearly all cases.
This is a general error that you get when the copier can't connect to a server on the network.
Check your network connections, and make sure no usernames or passwords that are used for authentication have changed.