Subject: Re: psycopg2: proper positioning of .commit() within try: except:
blocks

On 07/09/2024 16:48, Karsten Hilbert via Python-list wrote:

Dear all,

unto now I had been thinking this is a wise idiom (in code
that needs not care whether it fails to do what it tries to
do^1):

conn = psycopg2.connection(...)
curs = conn.cursor()
try:
curs.execute(SOME_SQL)
except PSYCOPG2-Exception:
some logging being done, and, yes, I
can safely inhibit propagation^1
finally:
conn.commit() # will rollback, if SOME_SQL failed
conn.close()

So today I head to learn that conn.commit() may very well
raise a DB related exception, too:

psycopg2.errors.SerializationFailure: could not serialize access due to read/write dependencies among transactions
DETAIL: Reason code: Canceled on identification as a pivot, during commit attempt.
TIP: The transaction might succeed if retried.

Now, what is the proper placement of the .commit() ?

(doing "with ... as conn:" does not free me of committing appropriately)

Should I

try:
curs.execute(SOME_SQL)
conn.commit()
except PSYCOPG2-Exception:
some logging being done, and, yes, I
can safely inhibit propagation^1
finally:
conn.close() # which should .rollback() automagically in case we had not reached to .commit()

?

Thanks for insights,
Karsten

I would put the curs.execute and the conn.commit in separate
try...except blocks.ÿ That way you know which one failed, and can put appropriate info in the log, which may help trouble-shooting.
(The general rule is to keep try...except blocks small.ÿ And of course
only catch the exceptions you are interested in, which you seem to be
already doing.)
Best wishes
Rob Cliffe

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Subject: Re: psycopg2: proper positioning of .commit() within try: except:
blocks

Am Sat, Sep 07, 2024 at 09:46:03AM -0700 schrieb Adrian Klaver:

unto now I had been thinking this is a wise idiom (in code
that needs not care whether it fails to do what it tries to
do^1):

conn =3D psycopg2.connection(...)

In the above do you have:

https://www.psycopg.org/docs/extensions.html#psycopg2.extensions.ISOLATI=

ON_LEVEL_SERIALIZABLE

psycopg2.extensions.ISOLATION_LEVEL_SERIALIZABLE

I do indeed.

Or is that in some other concurrent transaction?

In fact in that codebase all transactions -- running
concurrently or not -- are set to SERIALIZABLE.

They are not psycopg2.extensions.ISOLATION_LEVEL_AUTOCOMMIT,
for that matter.

curs =3D conn.cursor()
try:
curs.execute(SOME_SQL)
except PSYCOPG2-Exception:
some logging being done, and, yes, I
can safely inhibit propagation^1
finally:
conn.commit() # will rollback, if SOME_SQL failed

It will if you use with conn:, otherwise it up to you to do the rollback=

()

Are you are doing a rollback() in except PSYCOPG2-Exception: ?

No I don't but - to my understanding - an ongoing transaction
is being closed upon termination of the hosting connection.
Unless .commit() is explicitely being issued somewhere in the
code that closing of a transaction will amount to a ROLLBACK.

In case of SQL having failed within a given transaction a
COMMIT will fail-but-rollback, too (explicit ROLLBACK would
succeed while a COMMIT would fail and, in-effect, roll back).

IOW, when SOME_SQL has failed it won't matter that I close
the connection with conn.commit() and it won't matter that
conn.commit() runs a COMMIT on the database -- an open
transaction having run that failed SQL will still roll back
as if ROLLBACK had been issued. Or else my mental model is
wrong.

https://www.psycopg.org/docs/connection.html#connection.close

In the particular case I was writing about the SQL itself
succeeded but then the COMMIT failed due to serialization. I
was wondering about where to best place any needed
conn.commit(). My knee-jerk reaction was to then put it last
in the try: block...

All this is probably more related to Python than to PostgreSQL.

Thanks,
Karsten
=2D-
GPG 40BE 5B0E C98E 1713 AFA6 5BC0 3BEA AC80 7D4F C89B

--- MBSE BBS v1.0.8.4 (Linux-x86_64)
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Subject: Re: psycopg2: proper positioning of .commit() within try: except:
blocks

Am Sat, Sep 07, 2024 at 01:03:34PM -0700 schrieb Adrian Klaver:

In the case you show you are doing commit() before the close() so any er=

rors in the

transactions will show up then. My first thought would be to wrap the co=

mmit() in a

try/except and deal with error there.

Right, and this was suggested elsewhere ;)

And, yeah, the actual code is much more involved :-D

#------------------------------------------------------------------------
def __safely_close_cursor_and_rollback_close_conn(close_cursor=3DNone, rol= lback_tx=3DNone, close_conn=3DNone):
if close_cursor:
try:
close_cursor()
except PG_ERROR_EXCEPTION as pg_exc:
_log.exception('cannot close cursor')
gmConnectionPool.log_pg_exception_details(pg_exc)
if rollback_tx:
try:
# need to rollback so ABORT state isn't retained in pooled connections
rollback_tx()
except PG_ERROR_EXCEPTION as pg_exc:
_log.exception('cannot rollback transaction')
gmConnectionPool.log_pg_exception_details(pg_exc)
if close_conn:
try:
close_conn()
except PG_ERROR_EXCEPTION as pg_exc:
_log.exception('cannot close connection')
gmConnectionPool.log_pg_exception_details(pg_exc)

#------------------------------------------------------------------------
def run_rw_queries (
link_obj:_TLnkObj=3DNone,
queries:_TQueries=3DNone,
end_tx:bool=3DFalse,
return_data:bool=3DNone,
get_col_idx:bool=3DFalse,
verbose:bool=3DFalse
) -> tuple[list[dbapi.extras.DictRow], dict[str, int] | None]:
"""Convenience function for running read-write queries.

Typically (part of) a transaction.

Args:
link_obj: None, cursor, connection
queries:

* a list of dicts [{'cmd': <string>, 'args': <dict> or <tuple>)
* to be executed as a single transaction
* the last query may usefully return rows, such as:

SELECT currval('some_sequence');
or
INSERT/UPDATE ... RETURNING some_value;

end_tx:

* controls whether the transaction is finalized (eg.
COMMITted/ROLLed BACK) or not, this allows the
call to run_rw_queries() to be part of a framing
transaction
* if link_obj is a *connection* then "end_tx" will
default to False unless it is explicitly set to
True which is taken to mean "yes, you do have full
control over the transaction" in which case the
transaction is properly finalized
* if link_obj is a *cursor* we CANNOT finalize the
transaction because we would need the connection for that
* if link_obj is *None* "end_tx" will, of course, always
be True, because we always have full control over the
connection, not ending the transaction would be pointless

return_data:

* if true, the returned data will include the rows
the last query selected
* if false, it returns None instead

get_col_idx:

* True: the returned tuple will include a dictionary
mapping field names to column positions
* False: the returned tuple includes None instead of a field mapping dic=
tionary

Returns:

* (None, None) if last query did not return rows
* ("fetchall() result", <index>) if last query returned any rows and "re=
turn_data" was True

* for *index* see "get_col_idx"
"""
assert queries is not None, '<queries> must not be None'

if link_obj is None:
conn =3D get_connection(readonly =3D False)
curs =3D conn.cursor()
conn_close =3D conn.close
tx_commit =3D conn.commit
tx_rollback =3D conn.rollback
curs_close =3D curs.close
notices_accessor =3D conn
else:
conn_close =3D lambda *x: None
tx_commit =3D lambda *x: None
tx_rollback =3D lambda *x: None
curs_close =3D lambda *x: None
if isinstance(link_obj, dbapi._psycopg.cursor):
curs =3D link_obj
notices_accessor =3D curs.connection
elif isinstance(link_obj, dbapi._psycopg.connection):
if end_tx:
tx_commit =3D link_obj.commit
tx_rollback =3D link_obj.rollback
curs =3D link_obj.cursor()
curs_close =3D curs.close
notices_accessor =3D link_obj
else:
raise ValueError('link_obj must be cursor, connection or None but not [=
%s]' % link_obj)

for query in queries:
try:
args =3D query['args']
except KeyError:
args =3D None
try:
curs.execute(query['cmd'], args)
if verbose:
gmConnectionPool.log_cursor_state(curs)
for notice in notices_accessor.notices:
_log.debug(notice.replace('\n', '/').replace('\n', '/'))
del notices_accessor.notices[:]
# DB related exceptions
except dbapi.Error as pg_exc:
_log.error('query failed in RW connection')
gmConnectionPool.log_pg_exception_details(pg_exc)
for notice in notices_accessor.notices:
_log.debug(notice.replace('\n', '/').replace('\n', '/'))
del notices_accessor.notices[:]
__safely_close_cursor_and_rollback_close_conn (
curs_close,
tx_rollback,
conn_close
)
# privilege problem ?
if pg_exc.pgcode =3D=3D PG_error_codes.INSUFFICIENT_PRIVILEGE:
details =3D 'Query: [%s]' % curs.query.decode(errors =3D 'replace').st=
rip().strip('\n').strip().strip('\n')
if curs.statusmessage !=3D '':
details =3D 'Status: %s\n%s' % (
curs.statusmessage.strip().strip('\n').strip().strip('\n'),
details
)
if pg_exc.pgerror is None:
msg =3D '[%s]' % pg_exc.pgcode
else:
msg =3D '[%s]: %s' % (pg_exc.pgcode, pg_exc.pgerror)
raise gmExceptions.AccessDenied (
msg,
source =3D 'PostgreSQL',
code =3D pg_exc.pgcode,
details =3D details
)

# other DB problem
gmLog2.log_stack_trace()
raise

# other exception
except Exception:
_log.exception('error running query in RW connection')
gmConnectionPool.log_cursor_state(curs)
for notice in notices_accessor.notices:
_log.debug(notice.replace('\n', '/').replace('\n', '/'))
del notices_accessor.notices[:]
gmLog2.log_stack_trace()
__safely_close_cursor_and_rollback_close_conn (
curs_close,
tx_rollback,
conn_close
)
raise

data =3D None
col_idx =3D None
if return_data:
try:
data =3D curs.fetchall()
except Exception:
_log.exception('error fetching data from RW query')
gmLog2.log_stack_trace()
__safely_close_cursor_and_rollback_close_conn (
curs_close,
tx_rollback,
conn_close
)
raise

if get_col_idx:
col_idx =3D get_col_indices(curs)
curs_close()
tx_commit()
conn_close()
return (data, col_idx)

#------------------------------------------------------------------------


Best,
Karsten
=2D-
GPG 40BE 5B0E C98E 1713 AFA6 5BC0 3BEA AC80 7D4F C89B

--- MBSE BBS v1.0.8.4 (Linux-x86_64)
* Origin: ---:- FTN<->UseNet Gate -:--- (3:633/280.2@fidonet)

Subject: Re: psycopg2: proper positioning of .commit() within try: except:
blocks

Am Sat, Sep 07, 2024 at 02:09:28PM -0700 schrieb Adrian Klaver:

Right, and this was suggested elsewhere ;)

And, yeah, the actual code is much more involved :-D

I see that.

The question is does the full code you show fail?

The code sample you show in your original post is doing something very d=

ifferent then

what you show in your latest post. At this point I do not understand the=

exact problem

we are dealing with.

We are not dealing with an unsolved problem. I had been
asking for advice where to best place that .commit() call in
case I am overlooking benefits and drawbacks of choices.

The

try:
do something
except:
log something
finally:
.commit()

cadence is fairly Pythonic and elegant in that it ensures the
the .commit() will always be reached regardless of exceptions
being thrown or not and them being handled or not.

It is also insufficient because the .commit() itself may
elicit exceptions (from the database).

So there's choices:

Ugly:

try:
do something
except:
log something
finally:
try:
.commit()
except:
log some more

Fair but not feeling quite safe:

try:
do something
.commit()
except:
log something

Boring and repetitive and safe(r):

try:
do something
except:
log something
try:
.commit()
except:
log something

I eventually opted for the last version, except for factoring
out the second try: except: block.

Best,
Karsten
=2D-
GPG 40BE 5B0E C98E 1713 AFA6 5BC0 3BEA AC80 7D4F C89B

--- MBSE BBS v1.0.8.4 (Linux-x86_64)
* Origin: ---:- FTN<->UseNet Gate -:--- (3:633/280.2@fidonet)

Subject: Re: psycopg2: proper positioning of .commit() within try: except:
blocks

On 8/09/24 9:20 am, Karsten Hilbert wrote:

try:
do something
except:
log something
finally:
.commit()

cadence is fairly Pythonic and elegant in that it ensures the
the .commit() will always be reached regardless of exceptions
being thrown or not and them being handled or not.

That seems wrong to me. I would have thought the commit should only
be attempted if everything went right.

What if there's a problem in your code that causes a non-SQL-related
exception when some but not all of the SQL statements in the
transaction bave been issued? The database doesn't know something
has gone wrong, so it will happily commit a partially-completed
transaction and possibly corrupt your data.

This is how I normally do things like this:

try:
do something
.commit()
except:
log something
.rollback()

Doing an explicit rollback ensures that the transaction is always
rolled back if it is interrupted for any reason.

--
Greg

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Subject: Re: psycopg2: proper positioning of .commit() within try: except:
blocks

On 2024-09-08, Greg Ewing <greg.ewing@canterbury.ac.nz> wrote:

On 8/09/24 9:20 am, Karsten Hilbert wrote:

try:
do something
except:
log something
finally:
.commit()

cadence is fairly Pythonic and elegant in that it ensures the
the .commit() will always be reached regardless of exceptions
being thrown or not and them being handled or not.

That seems wrong to me. I would have thought the commit should only
be attempted if everything went right.

What if there's a problem in your code that causes a non-SQL-related exception when some but not all of the SQL statements in the
transaction bave been issued? The database doesn't know something
has gone wrong, so it will happily commit a partially-completed
transaction and possibly corrupt your data.

This is how I normally do things like this:

try:
do something
.commit()
except:
log something
.rollback()

Doing an explicit rollback ensures that the transaction is always
rolled back if it is interrupted for any reason.

What if there's an exception in your exception handler? I'd put the
rollback in the 'finally' handler, so it's always called. If you've
already called 'commit' then the rollback does nothing of course.

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Subject: Re: psycopg2: proper positioning of .commit() within try: except:
blocks

Am Sun, Sep 08, 2024 at 12:48:50PM +1200 schrieb Greg Ewing via Python-lis=
t:

On 8/09/24 9:20 am, Karsten Hilbert wrote:

try:
do something
except:
log something
finally:
.commit()

cadence is fairly Pythonic and elegant in that it ensures the
the .commit() will always be reached regardless of exceptions
being thrown or not and them being handled or not.

That seems wrong to me. I would have thought the commit should only
be attempted if everything went right.

What if there's a problem in your code that causes a non-SQL-related exception when some but not all of the SQL statements in the
transaction bave been issued? The database doesn't know something
has gone wrong, so it will happily commit a partially-completed
transaction and possibly corrupt your data.

A-ha !

try:
run_some_SQL_that_succeeds()
print(no_such_name) # tongue-in-cheek
1 / 0 # for good measure
except SOME_DB_ERROR:
print('some DB error, can be ignored for now')
finally:
commit()

which is wrong, given that the failing *Python* statements
may very well belong into the *business level* "transaction"
which a/the database transaction is part of.

See, that's why I was asking in the first place :-)

I was overlooking implications.

Karsten
=2D-
GPG 40BE 5B0E C98E 1713 AFA6 5BC0 3BEA AC80 7D4F C89B

--- MBSE BBS v1.0.8.4 (Linux-x86_64)
* Origin: ---:- FTN<->UseNet Gate -:--- (3:633/280.2@fidonet)

Subject: Re: psycopg2: proper positioning of .commit() within try: except:
blocks

Am Sun, Sep 08, 2024 at 12:48:50PM +1200 schrieb Greg Ewing via Python-lis=
t:

On 8/09/24 9:20 am, Karsten Hilbert wrote:

try:
do something
except:
log something
finally:
.commit()

cadence is fairly Pythonic and elegant in that it ensures the
the .commit() will always be reached regardless of exceptions
being thrown or not and them being handled or not.

That seems wrong to me. I would have thought the commit should only
be attempted if everything went right.

It is only attempted when "everything" went right. The fault
in my thinking was what the "everything" might encompass.
When some SQL fails it won't matter whether I say
conn.commit() or conn.rollback() or, in fact, nothing at all
=2D- the (DB !) transaction will be rolled back in any case.

However, that reasoning missed this:

What if there's a problem in your code that causes a non-SQL-related exception when some but not all of the SQL statements in the
transaction bave been [-- even successfully --] issued?

Still, in this code pattern:

try:
do something
.commit()
except:
log something

it doesn't technically matter whether I say .commit or .rollback here:

.rollback()

.... but ...

Doing an explicit rollback ensures that the transaction is always
rolled back if it is interrupted for any reason.

explicit is better than implicit ;-)

Karsten
=2D-
GPG 40BE 5B0E C98E 1713 AFA6 5BC0 3BEA AC80 7D4F C89B

--- MBSE BBS v1.0.8.4 (Linux-x86_64)
* Origin: ---:- FTN<->UseNet Gate -:--- (3:633/280.2@fidonet)

Subject: Re: psycopg2: proper positioning of .commit() within try: except:
blocks



On 07/09/2024 22:20, Karsten Hilbert via Python-list wrote:

Am Sat, Sep 07, 2024 at 02:09:28PM -0700 schrieb Adrian Klaver:

Right, and this was suggested elsewhere ;)

And, yeah, the actual code is much more involved :-D

I see that.

The question is does the full code you show fail?

The code sample you show in your original post is doing something very different then
what you show in your latest post. At this point I do not understand the exact problem
we are dealing with.

We are not dealing with an unsolved problem. I had been
asking for advice where to best place that .commit() call in
case I am overlooking benefits and drawbacks of choices.

The

try:
do something
except:
log something
finally:
.commit()

cadence is fairly Pythonic and elegant in that it ensures the
the .commit() will always be reached regardless of exceptions
being thrown or not and them being handled or not.

It is also insufficient because the .commit() itself may
elicit exceptions (from the database).

So there's choices:

Ugly:

try:
do something
except:
log something
finally:
try:
.commit()
except:
log some more

Fair but not feeling quite safe:

try:
do something
.commit()
except:
log something

Boring and repetitive and safe(r):

try:
do something
except:
log something
try:
.commit()
except:
log something

I eventually opted for the last version, except for factoring
out the second try: except: block.

Best,
Karsten
--
GPG 40BE 5B0E C98E 1713 AFA6 5BC0 3BEA AC80 7D4F C89B

Unless I'm missing something, the 1st & 3rd versions always do the
commit() even after the first bit fails, which seems wrong.
I suggest the 1st version but replacing "finally" by "else".ÿ Then the try-commit-except will not be executed if the "something" fails.
Perhaps the extra indentation of the second try block is a bit ugly, but
it is more important that it does the right thing.
If it is convenient (it may not be) to put the whole thing in a
function, you may feel that the follwing is less ugly:

try:
do something
except:
log something
return
try:
.commit()
except:
log some more
return

Best wishes
Rob Cliffe


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* Origin: ---:- FTN<->UseNet Gate -:--- (3:633/280.2@fidonet)

Subject: Re: psycopg2: proper positioning of .commit() within try: except:
blocks

Am Sun, Sep 08, 2024 at 02:58:03PM +0100 schrieb Rob Cliffe via Python-lis=
t:

Ugly:

try:
do something
except:
log something
finally:
try:
.commit()
except:
log some more

Fair but not feeling quite safe:

try:
do something
.commit()
except:
log something

Boring and repetitive and safe(r):

try:
do something
except:
log something
try:
.commit()
except:
log something

I eventually opted for the last version, except for factoring
out the second try: except: block.

Unless I'm missing something, the 1st & 3rd versions always do the commi=

t() even after

the first bit fails, which seems wrong.

Well, it does run a Python function called "commit". That
function will call "COMMIT" on the database. The end result
will be correct (at the SQL level) because the COMMIT will
not effect a durable commit of data when the SQL in "do
something" had failed.

We have, however, elicited that there may well be other
things belonging into the running business level transaction
which may fail and which should lead to data not being
committed despite being technically correct at the SQL level.

I suggest the 1st version but replacing "finally" by "else".=A0 Then the=

try-commit-except

will not be executed if the "something" fails.

The whole point was to consolidate the commit into one place.
It is unfortunately named, though. It should be called
"close_transaction".

Perhaps the extra indentation of the second try block is a bit ugly, but=

it is more

important that it does the right thing.
If it is convenient (it may not be) to put the whole thing in a function=

, you may feel

that the follwing is less ugly:

The whole thing does reside inside a function but the exit-early pattern

try:
do something
except:
log something
return
try:
.commit()
except:
log some more
return

won't help as there's more stuff to be done inside that function.

Thanks,
Karsten


For what it's worth here's the current state of code:

#------------------------------------------------------------------------
def __safely_close_cursor_and_rollback_close_conn(close_cursor=3DNone, rol= lback_tx=3DNone, close_conn=3DNone):
if close_cursor:
try:
close_cursor()
except PG_ERROR_EXCEPTION as pg_exc:
_log.exception('cannot close cursor')
gmConnectionPool.log_pg_exception_details(pg_exc)
if rollback_tx:
try:
# need to rollback so ABORT state isn't retained in pooled connections
rollback_tx()
except PG_ERROR_EXCEPTION as pg_exc:
_log.exception('cannot rollback transaction')
gmConnectionPool.log_pg_exception_details(pg_exc)
if close_conn:
try:
close_conn()
except PG_ERROR_EXCEPTION as pg_exc:
_log.exception('cannot close connection')
gmConnectionPool.log_pg_exception_details(pg_exc)

#------------------------------------------------------------------------
def __log_notices(notices_accessor=3DNone):
for notice in notices_accessor.notices:
_log.debug(notice.replace('\n', '/').replace('\n', '/'))
del notices_accessor.notices[:]

#------------------------------------------------------------------------
def __perhaps_reraise_as_permissions_error(pg_exc, curs):
if pg_exc.pgcode !=3D PG_error_codes.INSUFFICIENT_PRIVILEGE:
return

# privilege problem -- normalize as GNUmed exception
details =3D 'Query: [%s]' % curs.query.decode(errors =3D 'replace').strip=
().strip('\n').strip().strip('\n')
if curs.statusmessage !=3D '':
details =3D 'Status: %s\n%s' % (
curs.statusmessage.strip().strip('\n').strip().strip('\n'),
details
)
if pg_exc.pgerror is None:
msg =3D '[%s]' % pg_exc.pgcode
else:
msg =3D '[%s]: %s' % (pg_exc.pgcode, pg_exc.pgerror)
raise gmExceptions.AccessDenied (
msg,
source =3D 'PostgreSQL',
code =3D pg_exc.pgcode,
details =3D details
)

#------------------------------------------------------------------------
def run_rw_queries (
link_obj:_TLnkObj=3DNone,
queries:_TQueries=3DNone,
end_tx:bool=3DFalse,
return_data:bool=3DNone,
get_col_idx:bool=3DFalse,
verbose:bool=3DFalse
) -> tuple[list[dbapi.extras.DictRow], dict[str, int] | None]:
"""Convenience function for running read-write queries.

Typically (part of) a transaction.

Args:
link_obj: None, cursor, connection
queries:

* a list of dicts [{'cmd': <string>, 'args': <dict> or <tuple>)
* to be executed as a single transaction
* the last query may usefully return rows, such as:

SELECT currval('some_sequence');
or
INSERT/UPDATE ... RETURNING some_value;

end_tx:

* controls whether the transaction is finalized (eg.
COMMITted/ROLLed BACK) or not, this allows the
call to run_rw_queries() to be part of a framing
transaction
* if link_obj is a *connection* then "end_tx" will
default to False unless it is explicitly set to
True which is taken to mean "yes, you do have full
control over the transaction" in which case the
transaction is properly finalized
* if link_obj is a *cursor* we CANNOT finalize the
transaction because we would need the connection for that
* if link_obj is *None* "end_tx" will, of course, always
be True, because we always have full control over the
connection, not ending the transaction would be pointless

return_data:

* if true, the returned data will include the rows
the last query selected
* if false, it returns None instead

get_col_idx:

* True: the returned tuple will include a dictionary
mapping field names to column positions
* False: the returned tuple includes None instead of a field mapping dic=
tionary

Returns:

* (None, None) if last query did not return rows
* ("fetchall() result", <index>) if last query returned any rows and "re=
turn_data" was True

* for *index* see "get_col_idx"
"""
assert queries is not None, '<queries> must not be None'
assert isinstance(link_obj, (dbapi._psycopg.connection, dbapi._psycopg.cu=
rsor, type(None))), '<link_obj> must be None, a cursor, or a connection, b=
ut [%s] is of type (%s)' % (link_obj, type(link_obj))

if link_obj is None:
conn =3D get_connection(readonly =3D False)
curs =3D conn.cursor()
conn_close =3D conn.close
tx_commit =3D conn.commit
tx_rollback =3D conn.rollback
curs_close =3D curs.close
notices_accessor =3D conn
else:
conn_close =3D lambda *x: None
tx_commit =3D lambda *x: None
tx_rollback =3D lambda *x: None
curs_close =3D lambda *x: None
if isinstance(link_obj, dbapi._psycopg.cursor):
curs =3D link_obj
notices_accessor =3D curs.connection
elif isinstance(link_obj, dbapi._psycopg.connection):
curs =3D link_obj.cursor()
curs_close =3D curs.close
notices_accessor =3D link_obj
if end_tx:
tx_commit =3D link_obj.commit
tx_rollback =3D link_obj.rollback
for query in queries:
try:
args =3D query['args']
except KeyError:
args =3D None
try:
curs.execute(query['cmd'], args)
if verbose:
gmConnectionPool.log_cursor_state(curs)
__log_notices(notices_accessor)
# DB related exceptions
except dbapi.Error as pg_exc:
_log.error('query failed in RW connection')
gmConnectionPool.log_pg_exception_details(pg_exc)
__log_notices(notices_accessor)
__safely_close_cursor_and_rollback_close_conn (
curs_close,
tx_rollback,
conn_close
)
__perhaps_reraise_as_permissions_error(pg_exc, curs)
# not a permissions problem
gmLog2.log_stack_trace()
raise

# other exceptions
except Exception:
_log.exception('error running query in RW connection')
gmConnectionPool.log_cursor_state(curs)
__log_notices(notices_accessor)
gmLog2.log_stack_trace()
__safely_close_cursor_and_rollback_close_conn (
curs_close,
tx_rollback,
conn_close
)
raise

if not return_data:
curs_close()
tx_commit()
conn_close()
return (None, None)

data =3D None
try:
data =3D curs.fetchall()
except Exception:
_log.exception('error fetching data from RW query')
gmLog2.log_stack_trace()
__safely_close_cursor_and_rollback_close_conn (
curs_close,
tx_rollback,
conn_close
)
raise

col_idx =3D None
if get_col_idx:
col_idx =3D get_col_indices(curs)
curs_close()
tx_commit()
conn_close()
return (data, col_idx)

#------------------------------------------------------------------------

=2D-
GPG 40BE 5B0E C98E 1713 AFA6 5BC0 3BEA AC80 7D4F C89B

--- MBSE BBS v1.0.8.4 (Linux-x86_64)
* Origin: ---:- FTN<->UseNet Gate -:--- (3:633/280.2@fidonet)

Subject: Re: psycopg2: proper positioning of .commit() within try: except:
blocks

On 8/09/24 11:03 pm, Jon Ribbens wrote:

On 2024-09-08, Greg Ewing <greg.ewing@canterbury.ac.nz> wrote:

try:
do something
.commit()
except:
log something
.rollback()

What if there's an exception in your exception handler? I'd put the
rollback in the 'finally' handler, so it's always called.

Good point. Putting the rollback first would be safer/

--
Greg

--- MBSE BBS v1.0.8.4 (Linux-x86_64)
* Origin: ---:- FTN<->UseNet Gate -:--- (3:633/280.2@fidonet)

Subject: Re: psycopg2: proper positioning of .commit() within try: except:
blocks

On 9/09/24 2:13 am, Karsten Hilbert wrote:

For what it's worth here's the current state of code:

That code doesn't inspire much confidence in me. It's far too
convoluted with too much micro-management of exceptions.

I would much prefer to have just *one* place where exceptions are
caught and logged.

--
Greg

--- MBSE BBS v1.0.8.4 (Linux-x86_64)
* Origin: ---:- FTN<->UseNet Gate -:--- (3:633/280.2@fidonet)

Subject: Re: psycopg2: proper positioning of .commit() within try: except:
blocks

Am Mon, Sep 09, 2024 at 01:48:32PM +1200 schrieb Greg Ewing via Python-lis=
t:

That code doesn't inspire much confidence in me. It's far too
convoluted with too much micro-management of exceptions.

I would much prefer to have just *one* place where exceptions are
caught and logged.

I am open to suggestions.

Karsten
=2D-
GPG 40BE 5B0E C98E 1713 AFA6 5BC0 3BEA AC80 7D4F C89B

--- MBSE BBS v1.0.8.4 (Linux-x86_64)
* Origin: ---:- FTN<->UseNet Gate -:--- (3:633/280.2@fidonet)

Subject: Re: psycopg2: proper positioning of .commit() within try: except:
blocks

Am Mon, Sep 09, 2024 at 01:48:32PM +1200 schrieb Greg Ewing via Python-lis=
t:

That code doesn't inspire much confidence in me. It's far too
convoluted with too much micro-management of exceptions.

It is catching two exceptions, re-raising both of them,
except for re-raising one of them as another kind of
exception. What would you doing differently and how ?

I would much prefer to have just *one* place where exceptions are
caught and logged.

There's, of course, a top level handler which logs and user-displays-as-appropriate any exceptions. This is code
from a much larger codebase.

Karsten
=2D-
GPG 40BE 5B0E C98E 1713 AFA6 5BC0 3BEA AC80 7D4F C89B

--- MBSE BBS v1.0.8.4 (Linux-x86_64)
* Origin: ---:- FTN<->UseNet Gate -:--- (3:633/280.2@fidonet)