As a relatively unknown debugging tool for simulation tests, one could
have simulation print when a particular key is handled in various stages
of the commit process. This functionality was enabled by changing a 0
to a 1 in an #if, and changing a constant to the key in question.
As a proxy and storage server handle mutations, they call debugMutation
or debugKeyRange, which then checks against the mutation against the key
in question, and logs if they match. A mixture of printfs and
TraceEvents would then be emitted, and for this to actually be usable,
one also needs to comment out some particularly spammy debugKeyRange()
calls.
This PR reworks the API of debugMutation/debugKeyRange, pulls it out
into its own file, and trims what is logged by default into something
useful and understandable:
* debugMutation() now returns a TraceEvent, that one can add more details to before it is logged.
* Data distribution and storage server cleanup operations are no longer logged by default
atomicOp has an amplified performance overhead to the cluster,
for example, an ADD operation can be small, but SS has to load
the value to do the operation and the value can be large.
Adds CompareAndClear mutation. If the given parameter is equal to the
current value of the key, the key is cleared. At client, the mutation
is added to the operation stack. Hence if the mutation evaluates to
clear, we only get to know so when `read()` evaluates the stack in
`RYWIterator::kv()`, which is unlike what we currently do for typical
ClearRange.
Remove the use of relative paths. A header at foo/bar.h could be included by
files under foo/ with "bar.h", but would be included everywhere else as
"foo/bar.h". Adjust so that every include references such a header with the
latter form.
Signed-off-by: Robert Escriva <rescriva@dropbox.com>
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.
