When a client of the IDL tries to commit a read-modify-write transaction
but the database has changed in the meantime, the IDL tells its client to
wait for the IDL to change and then try the transaction again by returning
TXN_TRY_AGAIN. The "wait for the IDL to change" part is important because
there's no point in retrying the transaction before the IDL has received
the database updates (the transaction would fail in the same way all over
again).
However, the logic was incomplete: the database update can be received
*before* the reply to the transaction RPC (I think that in the current
ovsdb-server implementation this will always happen, in fact). When this
happens, the right thing to do is to retry the transaction immediately;
if we wait, then we're waiting for an additional change to the database
that may never come, causing an indefinite hang.
This commit therefore breaks the "try again" IDL commit status code
into two, one that means "try again immediately" and another that means
"wait for a change then try again". When an update is processed after a
transaction is committed but before the reply is received, the "try again
now" tells the IDL client not to wait for another database change before
retrying its transaction.
Bug #5980.
Reported-by: Ram Jothikumar <rjothikumar@nicira.com>
Reproduced-by: Alex Yip <alex@nicira.com>
This patch does minor style cleanups to the code in the python and
tests directory. There's other code floating around that could use
similar treatment, but updating it is not convenient at the moment.
Until now, the Python bindings for OVSDB have not supported writing to the
database. Instead, writes had to be done with "ovs-vsctl" subprocesses.
This commit adds write support and brings the Python bindings in line with
the C bindings.
This commit deletes the Python-specific IDL tests in favor of using the
same tests as the C version of the IDL, which now pass with both
implementations.
This commit updates the two users of the Python IDL to use the new write
support. I tested this updates only by writing unit tests for them,
which appear in upcoming commits.
According to Reid, there may be some disadvantages to having this class be
anonymous, for example, cannot do instance/typechecking, might be
allocating a new class for every row as well, which isn't the most memory
efficient.
Suggested-by: Reid Price <reid@nicira.com>
Idl.__parse_row_update() assumed that every change that the database server
sent down actually modified the database. This is generally true, but
since Idl.__modify_row() already returns whether there was a change, we
might as well use it.
Reported-by: Reid Price <reid@nicira.com>
Strangely malformed <row-update>s could hypothetically get confusing error
message. Using the Parser class should avoid that.
Reported-by: Reid Price <reid@nicira.com>
This leaves one use of __dict__ used for iterating through attributes.
I could use dir() instead, but I was put off by this note in its
documentation in the Python Library Reference:
Because dir() is supplied primarily as a convenience for use at an
interactive prompt, it tries to supply an interesting set of names more
than it tries to supply a rigorously or consistently defined set of names,
and its detailed behavior may change across releases. For example,
metaclass attributes are not in the result list when the argument is a
class.
Suggested-by: Reid Price <reid@nicira.com>
These initial bindings pass a few hundred of the corresponding tests
for C implementations of various bits of the Open vSwitch library API.
The poorest part of them is actually the Python IDL interface in
ovs.db.idl, which has not received enough attention yet. It appears
to work, but it doesn't yet support writes (transactions) and it is
difficult to use. I hope to improve it as it becomes clear what
semantics Python applications actually want from an IDL.
