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0c94a53a73
This is living in a subdirectory for now so we can have better
turnaround time on tests and not have to build everything else
along with it.
This covers the logic that we can have *without* actually using
databases or the filesystem in any way, just to provide a framework
that lets us validate the logic handling overlapping queries.
The overall purpose of this is to prevent deadlocks, by ensuring
that database locks are only taken when we have already proven
that they are available. In short, the QueryContext preregisters
its "scope" -- the set of things it may want to lock. The operation
of creating the QueryContext can block, but it blocks with no
database locks held. Once it is unblocked, the scope it has reported
is now considered unavailable, and no other QueryContext using any
overlapping scope can complete creation until this QueryContext
completes. While it's running, the QueryContext can't request write
access to anything outside its scope. Thus, once created, a
QueryContext can always proceed, without being blocked, until it's
done.
Note that this does not fully address multi-node behaviors;
once you have a QueryContext blocking things, you need to not
make queries to other nodes that could be blocked in turn by those
nodes. In short, no write queries to other nodes while holding a
write-type QueryContext on the local node, because if two nodes
do that to each other at once, they can both be blocked.
We believe RBF is currently designed such that read-only accesses
don't block progress on writes, so non-write access doesn't
create problems.
We also have some code to allow us to create dot-format output
from the components of this system, which is mostly intended to
be a debugging tool.
(cherry picked from commit
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|---|---|---|
| .. | ||
| testdata/fuzz/FuzzWriteRequests | ||
| doc.go | ||
| dot_test.go | ||
| query_context.go | ||
| query_context_test.go | ||
| rbf.go | ||
| TODO.txt | ||
| txstore.go | ||
| visualize.go | ||