Simulation identified the fact that we can violate the
VersionStamps-are-always-increasing promise via the following series of events:
1. On proxy 0, dumpData adds commit requests to proxy 0's commit promise stream
2. To any proxy, a client submits the first transaction of abortBackup, which stops further dumpData calls on proxy 0.
3. To any proxy that is not proxy 0, submit a transaction that checks if it needs to upgrade the destination version.
4. The transaction from (3) is committed
5. Transactions from (1) are committed
This is possible because the dumpData transactions have no read conflict
ranges, and thus it's impossible to make them abort due to "conflicting"
transactions. There's also no promise that if client C sends a commit to proxy
A, and later a client D sends a commit to proxy B, that B must log its commit
after A. (We only promise that if C is told it was committed before D is told
it was committed, then A committed before B.)
There was a failed attempt to fix this problem. We tried to add read conflict
ranges to dumpData transactions so that they could be aborted by "conflicting"
transactions. However, this failed because this now means that dumpData
transactions require conflict resolution, and the stale read version that they
use can cause them to be aborted with a transaction_too_old error.
(Transactions that don't have read conflict ranges will never return
transaction_too_old, because with no reads, the read snapshot version is
effectively meaningless.) This was never previously possible, so the existing
code doesn't retry commits, and to make things more complicated, the dumpData
commits must be applied in order. This would require either adding
dependencies to transactions (if A is going to commit then B must also be/have
committed), which would be complicated, or submitting transactions with a fixed
read version, and replaying the failed commits with a higher read version once
we get a transaction_too_old error, which would unacceptably slow down the
maximum throughput of dumpData.
Thus, we've instead elected to add a special transaction option that bypasses
proxy load balancing for commits, and always commits against proxy 0. We can
know for certain that after the transaction from (2) is committed, all of the
dumpData transactions that will be committed have been added to the commit
promise stream on proxy 0. Thus, if we enqueue another transaction against
proxy 0, we can know that it will be placed into the promise stream after all
of the dumpData transactions, thus providing the semantics that we require: no
dumpData transaction can commit after the destination version upgrade
transaction.
This means that loops like `seed=1; while ./fdbserver -r simulation -s $seed;
do seed=$(($seed+1)); done` to find an example of an often failing test. This
also means joshua will report ExitCode errors on anything that has a SevError
in the log.
As a part of this, we also implicitly downgrade any injected errors to SevWarnAlways.
If we're going to do the work to provide more optimized ways to zero files,
then I'd feel better with this being in a more common place, so that any other
zero-ers are likely to reuse it. It also makes testing easier/more obvious.
Also, because it's needed for correctness, fix the aligned_alloc for OSX, which
wasn't aligned, and use an actually aligned allocation function.
Several backup tasks have been cleaned up / simplified because they no longer need to manage the ‘raw’ structure of the backup. The addition of IBackupFile and its finish() method simplified the log and range writer tasks. Updated BlobStoreEndpoint to support now-required bucket creation and bucket listing prefix/delimiter options for finding common prefixes. Added KeyBackedSet<T> type. Moved JSONDoc to its own header. Added platform::findFilesRecursively().
Still to do: update command line tool to use new IBackupContainer interface, fix bugs in Restore startup.
Added an optimization to use a separate set for throttled events. Since this set is expected to be small, comparison of every event against this set is going to be cheaper.
std::is_pod<> being less restrictive than is_binary_serializable<> meant that
structs that both were POD and had a serialize method defined would be binary
serialized instead of using the defined serialize(). This means that it would
also serialize any padding that the struct contained, which would cause mass
waves of valgrind failures from uninitialized memory.
Included in this change is additional uses of valgrind client requests so that
attempts to send uninitialized memory are reported at the sending site, versus
as part of checksum calculation in sending the packet.
Evan Tschannen