This patch worked.
https://gerrit.sqlalchemy.org/#/c/zzzeek/sqlalchemy/+/747/
But I didn't get the log "Double checkin attempted", maybe the real working
code is
if connection_record and connection_record.fairy_ref is not None:
connection_record.checkin()
在 2018年5月16日星期三 UTC+8下午4:04:21，[email protected]写道：
>
> Thanks a lot.
>
> I'll test this patch in our environment.
>
> 在 2018年5月16日星期三 UTC+8上午2:58:56，Mike Bayer写道：
>>
>> good news, I reproduced it.
>>
>> Even better news for you, vindication! nothing to do with greenlets,
>> threads, concurrency, or anything (though it doesn't have to do with
>> the "del" or the weakref, this is much simpler ).
>>
>> This has to do with a special rule in the pool when there is a
>> so-called "reset agent" involved that cleans up a pooled connection
>> while taking into account the fact that the enclosing Connection had a
>> transaction in progress. That is introducing the
>> _handle_error()->invalidate() routine *inside* the normal
>> _finalize_fairy routine and that is why we see _finalize_fairy twice.
>> The _finalize_fairy we see that seems to start in the middle of the
>> operation is called first, then the _finalize_fairy we see failing is
>> inside of that. So they aren't sibling operations, they are nested.
>>
>>
>> https://bitbucket.org/zzzeek/sqlalchemy/issues/4252/double-checkin-due-to-handle_error-called
>>
>>
>>
>>
>> On Tue, May 15, 2018 at 1:26 PM, Mike Bayer <[email protected]>
>> wrote:
>> > can you add these lines to your logging, ensure that the check for
>> > "already in pool" is present, and produce new logs?
>> >
>> > try:
>> > fairy = fairy or _ConnectionFairy(
>> > connection, connection_record, echo)
>> > assert fairy.connection is connection
>> > pool.logger.debug("ABOUT TO RESET CONNECTION %s CONNECTION
>> > REC %s FAIRY %s", connection, fairy, connection_record)
>> > fairy._reset(pool)
>> > pool.logger.debug("COMPLETED RESET CONNECTION %s
>> > CONNECTION REC %s FAIRY %s", connection, fairy, connection_record)
>> >
>> > # Immediately close detached instances
>> > if not connection_record:
>> > pool._close_connection(connection)
>> > except BaseException as e:
>> > pool.logger.debug("EXCEPTION RAISED IN RESET CONNECTION %s
>> > CONNECTION REC %s FAIRY %s: %s", connection, fairy, connection_record,
>> > e)
>> > pool.logger.error(
>> > "Exception during reset or similar", exc_info=True)
>> > if connection_record:
>> > pool.logger.debug("jjs going to
>> connection_record.invalidate")
>> > connection_record.invalidate(e=e)
>> > if not isinstance(e, Exception):
>> > pool.logger.debug("jjs e %s is not Exception, raise
>> again", e)
>> > raise
>> >
>> > my current theory is that a greenlet is being blocked in _reset(),
>> > then waking up later but is being corrupted at the greenlet level in
>> > some way.
>> >
>> >
>> >
>> > On Tue, May 15, 2018 at 12:15 PM, Mike Bayer <[email protected]>
>> wrote:
>> >>
>> >>
>> >> On Tue, May 15, 2018, 3:26 AM <[email protected]> wrote:
>> >>>
>> >>> We got the log "jjs _finalize_fairy args" just once but the code in
>> >>> function _finalize_fairy seem to be called twice. It also confused
>> me.
>> >>
>> >>
>> >> It's because that code originated elsewhere and got blocked, then it
>> picks
>> >> up again but the callstack is somehow corrupted (or logging isn't
>> telling
>> >> the truth).
>> >>
>> >> Can you please give me:
>> >>
>> >> Exact version of eventlet in use
>> >> Exact version of psycopg2 and psyco-green
>> >> Exact python interpreter version
>> >> Exact version of SQLAlchemy
>> >> Exact version of Oslo.db
>> >>
>> >> Thanks
>> >>
>> >>
>> >>
>> >>>
>> >>> BTW, I tried to add code[1] to avoid double checkin in
>> _finalize_fairy but
>> >>> failed.
>> >>> That means the code in pool.py#L670-692 was called without L646-668.
>> >>>
>> >>> [1] https://github.com/jiajunsu/test_logs/blob/master/pool.py#L659
>> >>>
>> >>> 在 2018年5月15日星期二 UTC+8下午12:41:17，Mike Bayer写道：
>> >>>>
>> >>>> s
>> >>>>
>> >>>>
>> >>>>
>> >>>> On Mon, May 14, 2018 at 9:38 PM, <[email protected]> wrote:
>> >>>> > The tid is coroutine_id, we get it by id(greenlet.getcurrent()) in
>> each
>> >>>> > coroutine(green thread).
>> >>>> >
>> >>>> > We run nova-conductor with monkey_patch, the same as [1],
>> >>>> > eventlet.monkey_patch(os=False)
>> >>>> >
>> >>>> > Our nova-conductor is running with multi workers.
>> >>>> >
>> >>>> > It's confusing why the _finalize_fairy is called twice but only
>> log
>> >>>> > once at
>> >>>> > the entrance, that's why I guess it's called by weakref's
>> callback.
>> >>>>
>> >>>> For 130446032 which is the tid you mentioned, _finalize_fairy is
>> only
>> >>>> called once in your log:
>> >>>>
>> >>>> $ cat nc_5679.log | grep -e "130446032.*jjs _finalize"
>> >>>> 2018-05-14T11:11:39.955+08:00 localhost nova-conductor DEBUG
>> >>>> [pid:5679] [MainThread] [tid:130446032] [log.py:104 debug]
>> >>>> [req-841bb432-7cd2-4fa3-9def-559a34b05a21] jjs _finalize_fairy args
>> >>>> conn None, rec.conn None, rec, <sqlalchemy.pool._ConnectionRecord
>> >>>> object at 0x70cdb10>. ref None, fairy
>> >>>> <sqlalchemy.pool._ConnectionFairy object at 0x8a87390> debug
>> >>>>
>> >>>> Also, the log shows that no _finalize_fairy is ever called due to
>> >>>> "del" - this would show the weakref "ref" as non-None:
>> >>>>
>> >>>> $ cat nc_5679.log | grep -e "FINALIZE FAIRY.*REF:.*" | grep -v "REF:
>> >>>> None"
>> >>>> $
>> >>>>
>> >>>> I would assume by "finalize fairy" called twice, you're referring to
>> >>>> the fact that you see the "exception during reset or simlar"
>> message.
>> >>>> But that message is still AFAICT impossible to be emitted without
>> the
>> >>>> function being entered, and a corresponding "FINALIZE FAIRY" log
>> line
>> >>>> preceding it, unless something is going wrong with the logging, or
>> the
>> >>>> interpreter is somehow not functioning correctly (I wonder if
>> eventlet
>> >>>> had any such issues). I'm struggling to see any other possibility
>> >>>> but not coming up with any.
>> >>>>
>> >>>> One weird thing I'm trying to figure out is that I see a connection
>> >>>> being returned to the pool normally, but then nothing is logged
>> about
>> >>>> it after that:
>> >>>>
>> >>>> 2018-05-14T11:11:21.183+08:00 localhost nova-conductor DEBUG
>> >>>> [pid:5679] [MainThread] [tid:130446352] [log.py:104 debug]
>> >>>> [req-19a57f61-bc64-4575-8253-00b5bfe62a74] Connection <connection
>> >>>> object at 0x7f419c0; closed: 0> being returned to pool,
>> >>>> connection_record.connection <connection object at 0x7f419c0;
>> closed:
>> >>>> 0> debug
>> >>>>
>> >>>>
>> >>>> the next log message from tid:130446352 should be "jjs conn reset".
>> >>>> But that never happens. The next we see of that tid is:
>> >>>>
>> >>>> 2018-05-14T11:11:21.549+08:00 localhost nova-conductor DEBUG
>> >>>> [pid:5679] [MainThread] [tid:130446352] [log.py:104 debug]
>> >>>> [req-0ef61146-5cb6-4f46-9788-406b6d376843] jjs
>> >>>> _ConnectionFairy._checkout fariy None debug
>> >>>> 2018-05-14T11:11:21.549+08:00 localhost nova-conductor DEBUG
>> >>>> [pid:5679] [MainThread] [tid:130446352] [log.py:104 debug]
>> >>>> [req-0ef61146-5cb6-4f46-9788-406b6d376843] jjs before pool._do_get
>> >>>> pool queue deque([<sqlalchemy.pool._ConnectionRecord object at
>> >>>> 0x7777e10>, <sqlalchemy.pool._ConnectionRecord object at 0x75fb7d0>,
>> >>>> <sqlalchemy.pool._ConnectionRecord object at 0x778d810>,
>> >>>> <sqlalchemy.pool._ConnectionRecord object at 0x7600610>,
>> >>>> <sqlalchemy.pool._ConnectionRecord object at 0x6ea7e10>,
>> >>>> <sqlalchemy.pool._ConnectionRecord object at 0x7798050>,
>> >>>> <sqlalchemy.pool._ConnectionRecord object at 0x796d110>,
>> >>>> <sqlalchemy.pool._ConnectionRecord object at 0x7798d50>,
>> >>>> <sqlalchemy.pool._ConnectionRecord object at 0x75f5710>]) debug
>> >>>>
>> >>>> that is, it's checking out a new connection ? If it were blocking
>> on
>> >>>> trying to reset the connection, we wouldn't see that tid again. I
>> >>>> wonder if the greenlet was interrupted or something. I'm finding
>> >>>> various impossibilities like this going on and not able to come up
>> >>>> with any theory other than the interpreter is somehow not
>> functioning
>> >>>> correcltly, or the logging here is somehow incomplete.
>> >>>>
>> >>>> I notice you're on a very old version of SQLAlchemy (three years
>> old).
>> >>>> You really should be on at least the 1.1 series because for
>> >>>> greenlets you need to have:
>> >>>>
>> >>>>
>> http://docs.sqlalchemy.org/en/latest/changelog/migration_11.html#change-3803.
>>
>>
>> >>>>
>> >>>>
>> >>>>
>> >>>>
>> >>>>
>> >>>>
>> >>>>
>> >>>>
>> >>>> >
>> >>>> > [1]
>> https://github.com/openstack/nova/blob/master/nova/cmd/__init__.py
>> >>>> >
>> >>>> >
>> >>>> > 在 2018年5月14日星期一 UTC+8下午11:59:43，Mike Bayer写道：
>> >>>> >>
>> >>>> >> I notice in this log file there are multiple "tid", which I
>> assume to
>> >>>> >> be thread identifiers ? E.g. OS-level threads? Are you using
>> >>>> >> eventlet or not? Are you monkeypatching SQLAlchemy and then
>> using
>> >>>> >> multiple OS-level threads at the same time? Because that likely
>> >>>> >> doesn't work.
>> >>>> >>
>> >>>> >> Particularly, the log here illustrates an impossible codepath.
>> >>>> >>
>> >>>> >> We enter finalize_fairy with connection is None:
>> >>>> >>
>> >>>> >> 2018-05-14T11:11:39.961+08:00 localhost nova-conductor DEBUG
>> >>>> >> [pid:5679] [MainThread] [tid:130446352] [log.py:104 debug]
>> >>>> >> [req-74ef6531-2d92-40ea-a524-f54e11edab06] FINALIZE FAIRY: DB
>> CONN:
>> >>>> >> None, FAIRY: <sqlalchemy.pool._ConnectionFairy object at
>> 0x87dd3d0>,
>> >>>> >> REF: None CONNECTION_REC: <sqlalchemy.pool._ConnectionRecord
>> object
>> >>>> >> at 0x776fe90> CONNECTION_REC REF <weakref at 0x7c5cdb8; to
>> >>>> >> '_ConnectionFairy' at 0x87dd3d0> debug
>> >>>> >>
>> >>>> >> this seems to make it through to the checkin at the bottom.
>> >>>> >>
>> >>>> >> Then, we see this:
>> >>>> >>
>> >>>> >> 2018-05-14T11:11:39.968+08:00 localhost nova-conductor ERROR
>> >>>> >> [pid:5679] [MainThread] [tid:130446032] [log.py:122 error]
>> >>>> >> [req-841bb432-7cd2-4fa3-9def-559a34b05a21] Exception during reset
>> or
>> >>>> >> similar
>> >>>> >>
>> >>>> >> The only place that message is generated is *in* finalize_fairy,
>> >>>> >> *before* the checkin occurs, and *only* if _finalize_fairy was
>> called
>> >>>> >> *with* a connection that is non -None. There is no other call
>> >>>> >> _finalize_fairy with that request identifier, therefore I see no
>> >>>> >> evidence of where this message "exception during reset" can be
>> >>>> >> generated from - there would at least need to be an additional
>> log
>> >>>> >> line with "FINALIZE FAIRY" and the connection non-None for this
>> to be
>> >>>> >> reached. I see no way that the pool.py shipped with SQLAlchemy
>> can
>> >>>> >> possibly generate this series of steps.
>> >>>> >>
>> >>>> >> This is an extremely intricate issue and I still have only the
>> vaguest
>> >>>> >> notion of how you are running SQLAlchemy / Nova.
>> >>>> >>
>> >>>> >>
>> >>>> >>
>> >>>> >>
>> >>>> >> On Mon, May 14, 2018 at 11:10 AM, Mike Bayer <
>> [email protected]>
>> >>>> >> wrote:
>> >>>> >> > OK I need the exact pool.py you are using as well that includes
>> all
>> >>>> >> > these logging statements and any other adjustments that were
>> made.
>> >>>> >> >
>> >>>> >> >
>> >>>> >> >
>> >>>> >> > On Mon, May 14, 2018 at 8:02 AM, <[email protected]> wrote:
>> >>>> >> >> I've uploaded the logs here:
>> >>>> >> >>
>> >>>> >> >>
>> https://raw.githubusercontent.com/jiajunsu/test_logs/master/nc_5679.log
>> >>>> >> >>
>> >>>> >> >> The ConnectionRecord is 0x70cdb10, tid(coroutine id) is
>> 130446032
>> >>>> >> >>
>> >>>> >> >> At 2018-05-14T11:11:39.970, we got the log " jjs rec already
>> in
>> >>>> >> >> pool
>> >>>> >> >> checkin", but I just deleted `return` in code, so the problem
>> >>>> >> >> happen
>> >>>> >> >> again.
>> >>>> >> >>
>> >>>> >> >>
>> >>>> >> >>
>> >>>> >> >>
>> >>>> >> >> 在 2018年5月14日星期一 UTC+8上午10:48:49，Mike Bayer写道：
>> >>>> >> >>>
>> >>>> >> >>> as well as the log that shows this:
>> >>>> >> >>>
>> >>>> >> >>> + if self in pool._pool.queue:
>> >>>> >> >>> + pool.logger.debug("jjs rec already in pool checkin,
>> skip
>> >>>> >> >>> %r",
>> >>>> >> >>> self)
>> >>>> >> >>> + return
>> >>>> >> >>>
>> >>>> >> >>>
>> >>>> >> >>> actually happening.
>> >>>> >> >>>
>> >>>> >> >>>
>> >>>> >> >>>
>> >>>> >> >>>
>> >>>> >> >>> On Sun, May 13, 2018 at 10:42 PM, Mike Bayer
>> >>>> >> >>> <[email protected]>
>> >>>> >> >>> wrote:
>> >>>> >> >>> > On Sun, May 13, 2018 at 10:35 PM, <[email protected]>
>> wrote:
>> >>>> >> >>> >> "jjs" is short for my name and "cjr" is my
>> colleague's(JinRong
>> >>>> >> >>> >> Cai). We
>> >>>> >> >>> >> work
>> >>>> >> >>> >> together and add logs in the same environment, add prefix
>> of
>> >>>> >> >>> >> name
>> >>>> >> >>> >> to
>> >>>> >> >>> >> get a
>> >>>> >> >>> >> keyword for log filter.
>> >>>> >> >>> >>
>> >>>> >> >>> >> The doubled ConnectionRecords(with None connection) are
>> got by
>> >>>> >> >>> >> two
>> >>>> >> >>> >> different
>> >>>> >> >>> >> coroutines, and the variable record.connection is rewrite
>> by
>> >>>> >> >>> >> the
>> >>>> >> >>> >> second
>> >>>> >> >>> >> coroutines.
>> >>>> >> >>> >> After the record being put back to QueuePool again, there
>> are
>> >>>> >> >>> >> two
>> >>>> >> >>> >> same
>> >>>> >> >>> >> record with same connection in the pool, which will cause
>> the
>> >>>> >> >>> >> next
>> >>>> >> >>> >> two
>> >>>> >> >>> >> coroutines get conflict and deadlock in psycopg2 as above.
>> >>>> >> >>> >
>> >>>> >> >>> > OK, I need the detailed step by step that shows how the two
>> >>>> >> >>> > coroutines
>> >>>> >> >>> > are interacting such that they both are returning the same
>> >>>> >> >>> > connection.
>> >>>> >> >>> > The nova log above seems to show just one coroutine I
>> assume
>> >>>> >> >>> > since
>> >>>> >> >>> > there is just one nova request ID, if I understand
>> correctly.
>> >>>> >> >>> >
>> >>>> >> >>> >>
>> >>>> >> >>> >> The logs of psycopg2 has been pasted at
>> >>>> >> >>> >> https://github.com/psycopg/psycopg2/issues/703
>> >>>> >> >>> >
>> >>>> >> >>> > The above issue says the bug has been found in SQLAlchemy
>> but
>> >>>> >> >>> > there
>> >>>> >> >>> > is
>> >>>> >> >>> > no bug report yet and I've not yet been shown how the
>> behavior
>> >>>> >> >>> > here
>> >>>> >> >>> > is
>> >>>> >> >>> > possible. I posted a straightforward example above,
>> can you
>> >>>> >> >>> > please show me where the two coroutines get mixed up ?
>> >>>> >> >>> >
>> >>>> >> >>> >
>> >>>> >> >>> >
>> >>>> >> >>> >
>> >>>> >> >>> >>
>> >>>> >> >>> >>
>> >>>> >> >>> >>
>> >>>> >> >>> >> 在 2018年5月11日星期五 UTC+8上午3:05:46，Mike Bayer写道：
>> >>>> >> >>> >>>
>> >>>> >> >>> >>> I tried to follow your log lines, which is difficult
>> because I
>> >>>> >> >>> >>> don't
>> >>>> >> >>> >>> know where those log statements actually are and I don't
>> know
>> >>>> >> >>> >>> what
>> >>>> >> >>> >>> acronyms like "jjs", "cjr", mean. But it does look like
>> it's
>> >>>> >> >>> >>> al
>> >>>> >> >>> >>> in
>> >>>> >> >>> >>> one thread (so not async GC) and all in one Nova request
>> (so
>> >>>> >> >>> >>> perhaps
>> >>>> >> >>> >>> just one greenlet involved, unless other greenlets are
>> >>>> >> >>> >>> affecting
>> >>>> >> >>> >>> this
>> >>>> >> >>> >>> without them being displayed in this log snippet). I do
>> see
>> >>>> >> >>> >>> the
>> >>>> >> >>> >>> connection record doubled at the end. So here is the
>> >>>> >> >>> >>> illustration of
>> >>>> >> >>> >>> those steps in isolation, the connection record is not
>> >>>> >> >>> >>> doubled.
>> >>>> >> >>> >>> Can
>> >>>> >> >>> >>> you alter this program to show this condition occurring?
>> >>>> >> >>> >>>
>> >>>> >> >>> >>> from sqlalchemy import create_engine
>> >>>> >> >>> >>>
>> >>>> >> >>> >>> e =
>> create_engine("postgresql://scott:tiger@localhost/test",
>> >>>> >> >>> >>> echo_pool='debug')
>> >>>> >> >>> >>> e.connect().close()
>> >>>> >> >>> >>>
>> >>>> >> >>> >>> assert len(e.pool._pool.queue) == 1
>> >>>> >> >>> >>>
>> >>>> >> >>> >>> c1 = e.connect()
>> >>>> >> >>> >>>
>> >>>> >> >>> >>> assert len(e.pool._pool.queue) == 0
>> >>>> >> >>> >>>
>> >>>> >> >>> >>> c1.engine.pool._invalidate(c1._Connection__connection,
>> None)
>> >>>> >> >>> >>> c1.invalidate(e)
>> >>>> >> >>> >>>
>> >>>> >> >>> >>> # connection record is back
>> >>>> >> >>> >>> assert len(e.pool._pool.queue) == 1
>> >>>> >> >>> >>>
>> >>>> >> >>> >>> # do a reconnect
>> >>>> >> >>> >>> c1.connection
>> >>>> >> >>> >>>
>> >>>> >> >>> >>> # uses the record again
>> >>>> >> >>> >>> assert len(e.pool._pool.queue) == 0
>> >>>> >> >>> >>>
>> >>>> >> >>> >>> # close the Connection
>> >>>> >> >>> >>> c1.close()
>> >>>> >> >>> >>>
>> >>>> >> >>> >>> # record is back
>> >>>> >> >>> >>> assert len(e.pool._pool.queue) == 1
>> >>>> >> >>> >>>
>> >>>> >> >>> >>> # etc.
>> >>>> >> >>> >>> c1 = e.connect()
>> >>>> >> >>> >>> assert len(e.pool._pool.queue) == 0
>> >>>> >> >>> >>>
>> >>>> >> >>> >>> c1.close()
>> >>>> >> >>> >>> assert len(e.pool._pool.queue) == 1
>> >>>> >> >>> >>>
>> >>>> >> >>> >>>
>> >>>> >> >>> >>>
>> >>>> >> >>> >>>
>> >>>> >> >>> >>> On Thu, May 10, 2018 at 12:25 PM, Mike Bayer
>> >>>> >> >>> >>> <[email protected]>
>> >>>> >> >>> >>> wrote:
>> >>>> >> >>> >>> > Here's a print statement you might want to try:
>> >>>> >> >>> >>> >
>> >>>> >> >>> >>> > diff --git a/lib/sqlalchemy/pool.py
>> b/lib/sqlalchemy/pool.py
>> >>>> >> >>> >>> > index 89a4cea7c..452db4883 100644
>> >>>> >> >>> >>> > --- a/lib/sqlalchemy/pool.py
>> >>>> >> >>> >>> > +++ b/lib/sqlalchemy/pool.py
>> >>>> >> >>> >>> > @@ -689,6 +689,19 @@ def _finalize_fairy(connection,
>> >>>> >> >>> >>> > connection_record,
>> >>>> >> >>> >>> > been garbage collected.
>> >>>> >> >>> >>> >
>> >>>> >> >>> >>> > """
>> >>>> >> >>> >>> > + print(
>> >>>> >> >>> >>> > + "FINALIZE FAIRY: GREENLET ID: %s, DB CONN:
>> %s,
>> >>>> >> >>> >>> > FAIRY:
>> >>>> >> >>> >>> > %s,
>> >>>> >> >>> >>> > REF:
>> >>>> >> >>> >>> > %s "
>> >>>> >> >>> >>> > + "CONNECTION_REC: %s CONNECTION_REC REF %s" % (
>> >>>> >> >>> >>> > + "put greenlet id here",
>> >>>> >> >>> >>> > + connection,
>> >>>> >> >>> >>> > + fairy,
>> >>>> >> >>> >>> > + ref,
>> >>>> >> >>> >>> > + connection_record,
>> >>>> >> >>> >>> > + connection_record.fairy_ref
>> >>>> >> >>> >>> > + if connection_record is not None else
>> "n/a"
>> >>>> >> >>> >>> > + )
>> >>>> >> >>> >>> > + )
>> >>>> >> >>> >>> > +
>> >>>> >> >>> >>> > _refs.discard(connection_record)
>> >>>> >> >>> >>> >
>> >>>> >> >>> >>> > if ref is not None:
>> >>>> >> >>> >>> >
>> >>>> >> >>> >>> >
>> >>>> >> >>> >>> >
>> >>>> >> >>> >>> >
>> >>>> >> >>> >>> >
>> >>>> >> >>> >>> > On Thu, May 10, 2018 at 12:21 PM, Mike Bayer
>> >>>> >> >>> >>> > <[email protected]>
>> >>>> >> >>> >>> > wrote:
>> >>>> >> >>> >>> >> On Thu, May 10, 2018 at 7:23 AM, <[email protected]>
>>
>> >>>> >> >>> >>> >> wrote:
>> >>>> >> >>> >>> >>> Hi Mike,
>> >>>> >> >>> >>> >>>
>> >>>> >> >>> >>> >>> I added more logs and finnaly find the reason and a
>> method
>> >>>> >> >>> >>> >>> to
>> >>>> >> >>> >>> >>> avoid
>> >>>> >> >>> >>> >>> the
>> >>>> >> >>> >>> >>> deadlock between coroutines.
>> >>>> >> >>> >>> >>>
>> >>>> >> >>> >>> >>> In summary, the deadlock happend because two
>> different
>> >>>> >> >>> >>> >>> coroutines
>> >>>> >> >>> >>> >>> use
>> >>>> >> >>> >>> >>> the
>> >>>> >> >>> >>> >>> same ConnectionRecord with same connection.
>> >>>> >> >>> >>> >>> It happends under QueuePool, when the DB connections
>> are
>> >>>> >> >>> >>> >>> reset
>> >>>> >> >>> >>> >>> by
>> >>>> >> >>> >>> >>> the
>> >>>> >> >>> >>> >>> DB
>> >>>> >> >>> >>> >>> server(not related with the backend driver).
>> >>>> >> >>> >>> >>>
>> >>>> >> >>> >>> >>> 1.A coroutine get a ConnectionRecord into
>> ConnectionFairy,
>> >>>> >> >>> >>> >>> and
>> >>>> >> >>> >>> >>> apply a
>> >>>> >> >>> >>> >>> weakref of the ConnectionFairy, with callback
>> function
>> >>>> >> >>> >>> >>> `_finalize_fairy`.
>> >>>> >> >>> >>> >>> 2.When the connection get disconnected, it receives
>> an
>> >>>> >> >>> >>> >>> exception(psycopg2.OperationalError), and goto
>> >>>> >> >>> >>> >>> Connection._handle_dbapi_exception.
>> >>>> >> >>> >>> >>> 3.In `_handle_dbapi_exception.finnaly`, it will call
>> both
>> >>>> >> >>> >>> >>> `ConnectionFairy.invalidate` and `self.invalidate`.
>> >>>> >> >>> >>> >>> 4.In `ConnectionFairy.invalidate`,
>> >>>> >> >>> >>> >>> `_ConnectionRecord._checkin` is
>> >>>> >> >>> >>> >>> called,
>> >>>> >> >>> >>> >>> and put the ConnectionRecord back to the QueuePool.
>> >>>> >> >>> >>> >>> 5.In `self.invalidate`, `del self._root.__connection`
>> is
>> >>>> >> >>> >>> >>> called,
>> >>>> >> >>> >>> >>> and
>> >>>> >> >>> >>> >>> **del**
>> >>>> >> >>> >>> >>> the ConnectionFairy.
>> >>>> >> >>> >>> >>> 6.The **del** operation will make weakref of
>> >>>> >> >>> >>> >>> ConnectionFairy
>> >>>> >> >>> >>> >>> to
>> >>>> >> >>> >>> >>> dead,
>> >>>> >> >>> >>> >>> and
>> >>>> >> >>> >>> >>> the callback `_finalize_fairy` executed.
>> >>>> >> >>> >>> >>> 7.In `_finalize_fairy`, another
>> >>>> >> >>> >>> >>> `_ConnectionRecord._checkin`
>> >>>> >> >>> >>> >>> is
>> >>>> >> >>> >>> >>> called, put
>> >>>> >> >>> >>> >>> the ConnectionRecord to the QueuePool again.
>> >>>> >> >>> >>> >>
>> >>>> >> >>> >>> >> Here's what does not make sense. You are claiming
>> that a
>> >>>> >> >>> >>> >> simple
>> >>>> >> >>> >>> >> invalidation will result in the same ConnectionRecord
>> being
>> >>>> >> >>> >>> >> checked
>> >>>> >> >>> >>> >> in
>> >>>> >> >>> >>> >> twice. This is obviously not the case, what is
>> special in
>> >>>> >> >>> >>> >> your
>> >>>> >> >>> >>> >> situation that makes this happen?
>> >>>> >> >>> >>>
>
>
--
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The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
To post example code, please provide an MCVE: Minimal, Complete, and Verifiable
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