[psycopg] 2.7.2 still problem with readonly/autocommit, was: Changingset_session implementation

While the below tests had been run with 2.7.1 the problem
persists with 2.7.3.

I am again attaching the script for reproducing the problem.

Can anyone test, reproduce, suggest a fix ?

Thanks,
Karsten


On Mon, Aug 07, 2017 at 10:35:26PM +0200, Karsten Hilbert wrote:

> has anyone been able to reproduce the problem described
> below?  I'd be glad to provide more information if needed.
>
> Thanks !
>
> Karsten
>
>
> On Thu, Aug 03, 2017 at 11:08:18PM +0200, Karsten Hilbert wrote:
>
> > Regarding the below problem with readwrite autocommit
> > connections in default-readonly databases I have whittled
> > down a test case to the following (attached):
> >
> >     db = u'gnumed_v20'        # a database configured "alter database %s set default_transaction_read_only to on"
> >     user = 'gm-dbo'            # a user with CREATE DATABASE powers
> >
> >     cmd_def_tx_ro = "SELECT upper(source), name, upper(setting) FROM pg_settings WHERE name =
'default_transaction_read_only'"
> >     cmd_create_db = "create database %s_copy template %s" % (db, db)
> >
> >     import sys
> >     import psycopg2
> >
> >     conn = psycopg2.connect(dbname = db, user = user)
> >     print 'conn:', conn
> >     print 'readonly:', conn.readonly
> >     print 'autocommit:', conn.autocommit
> >     conn.autocommit = False
> >     conn.readonly = False                            # <========== comment out for success
> >     conn.autocommit = True
> >     print 'autocommit now:', conn.autocommit
> >     conn.readonly = False
> >     print 'readonly now:', conn.readonly
> >     curs = conn.cursor()
> >     curs.execute(cmd_def_tx_ro)
> >     print 'should show DEFAULT_TRANSACTION_READ_ONLY set to ON'
> >     print curs.fetchall()
> >     curs.close()
> >     conn.commit()
> >     print 'the following CREATE DATABASE should fail'
> >     curs = conn.cursor()
> >     try:
> >         curs.execute(cmd_create_db)
> >     except psycopg2.InternalError as ex:
> >         print 'SQL failed:'
> >         print ex
> >
> >     print 'shutting down'
> >
> >     curs.close()
> >     conn.rollback()
> >     conn.close()
> >
> > which shows on the console:
> >
> >     ncq@hermes:~$ python x-test-default_ro.py
> >     conn: <connection object at 0xb674e6bc; dsn: 'dbname=gnumed_v20 user=gm-dbo', closed: 0>
> >     readonly: None
> >     autocommit: False
> >     autocommit now: True
> >     readonly now: False
> >     should show DEFAULT_TRANSACTION_READ_ONLY set to ON
> >     [('DATABASE', 'default_transaction_read_only', 'ON')]
> >     the following CREATE DATABASE should fail
> >     SQL failed:
> >     cannot execute CREATE DATABASE in a read-only transaction
> >
> >     shutting down
> >
> > The PostgreSQL log shows:
> >
> >     2017-08-03 21:00:19 GMT LOG:  00000: Verbindung empfangen: Host=[local]
> >     2017-08-03 21:00:19 GMT ORT:  BackendInitialize, postmaster.c:4135
> >     2017-08-03 21:00:19 GMT LOG:  00000: Verbindung autorisiert: Benutzer=gm-dbo Datenbank=gnumed_v20
> >     2017-08-03 21:00:19 GMT ORT:  PerformAuthentication, postinit.c:272
> >     2017-08-03 21:00:19 GMT LOG:  00000: statement: SELECT upper(source), name, upper(setting) FROM pg_settings
WHEREname = 'default_transaction_read_only' 
> >     2017-08-03 21:00:19 GMT LOCATION:  exec_simple_query, postgres.c:935
> >     2017-08-03 21:00:19 GMT LOG:  00000: statement: create database gnumed_v20_copy template gnumed_v20
> >     2017-08-03 21:00:19 GMT LOCATION:  exec_simple_query, postgres.c:935
> >     2017-08-03 21:00:19 GMT ERROR:  25006: cannot execute CREATE DATABASE in a read-only transaction
> >     2017-08-03 21:00:19 GMT LOCATION:  PreventCommandIfReadOnly, utility.c:236
> >     2017-08-03 21:00:19 GMT STATEMENT:  create database gnumed_v20_copy template gnumed_v20
> >     2017-08-03 21:00:19 GMT LOG:  00000: disconnection: session time: 0:00:00.007 user=gm-dbo database=gnumed_v20
host=[local]
> >     2017-08-03 21:00:19 GMT LOCATION:  log_disconnections, postgres.c:4501
> >
> > Commenting out the marked line makes it work and the log shows:
> >
> >     2017-08-03 21:01:24 GMT LOG:  00000: Verbindung empfangen: Host=[local]
> >     2017-08-03 21:01:24 GMT ORT:  BackendInitialize, postmaster.c:4135
> >     2017-08-03 21:01:24 GMT LOG:  00000: Verbindung autorisiert: Benutzer=postgres Datenbank=postgres
> >     2017-08-03 21:01:24 GMT ORT:  PerformAuthentication, postinit.c:272
> >     2017-08-03 21:01:25 GMT LOG:  00000: Anweisung: drop database gnumed_v20_copy ;
> >     2017-08-03 21:01:25 GMT ORT:  exec_simple_query, postgres.c:935
> >     2017-08-03 21:01:26 GMT LOG:  00000: Verbindungsende: Sitzungszeit: 0:00:02.324 Benutzer=postgres
Datenbank=postgresHost=[local] 
> >     2017-08-03 21:01:26 GMT ORT:  log_disconnections, postgres.c:4501
> >     2017-08-03 21:01:33 GMT LOG:  00000: Verbindung empfangen: Host=[local]
> >     2017-08-03 21:01:33 GMT ORT:  BackendInitialize, postmaster.c:4135
> >     2017-08-03 21:01:33 GMT LOG:  00000: Verbindung autorisiert: Benutzer=gm-dbo Datenbank=gnumed_v20
> >     2017-08-03 21:01:33 GMT ORT:  PerformAuthentication, postinit.c:272
> >     2017-08-03 21:01:33 GMT LOG:  00000: statement: SET default_transaction_read_only TO 'off'
> >     2017-08-03 21:01:33 GMT LOCATION:  exec_simple_query, postgres.c:935
> >     2017-08-03 21:01:33 GMT LOG:  00000: statement: SELECT upper(source), name, upper(setting) FROM pg_settings
WHEREname = 'default_transaction_read_only' 
> >     2017-08-03 21:01:33 GMT LOCATION:  exec_simple_query, postgres.c:935
> >     2017-08-03 21:01:33 GMT LOG:  00000: statement: create database gnumed_v20_copy template gnumed_v20
> >     2017-08-03 21:01:33 GMT LOCATION:  exec_simple_query, postgres.c:935
> >     2017-08-03 21:01:37 GMT LOG:  00000: duration: 3447.360 ms
> >     2017-08-03 21:01:37 GMT LOCATION:  exec_simple_query, postgres.c:1164
> >     2017-08-03 21:01:37 GMT LOG:  00000: disconnection: session time: 0:00:03.454 user=gm-dbo database=gnumed_v20
host=[local]
> >     2017-08-03 21:01:37 GMT LOCATION:  log_disconnections, postgres.c:4501
> >
> > So, under some circumstances psycopg2 does send the
> >
> >     2017-08-03 21:01:33 GMT LOG:  00000: statement: SET default_transaction_read_only TO 'off'
> >
> > while sometimes it does not, despite both times being in
> > autocommit=True and readonly=False when the "create database"
> > is sent.
> >
> > Of course, the
> >
> >     conn.autocommit = False
> >     conn.readonly = False                            # <========== comment out for success
> >     conn.autocommit = True
> >     conn.readonly = False
> >
> > seems redundant but that is the relevant sequence of events
> > condensed from a larger body of code. Redundant as it may
> > seem it should still work, no ?
> >
> > I am not sure I fully grok what is happening...
> >
> > Thanks for insights,
> > Karsten
> >
> >
> > On Wed, Aug 02, 2017 at 09:38:21PM +0200, Karsten Hilbert wrote:
> >
> > > On Wed, Aug 02, 2017 at 03:10:15PM +0100, Daniele Varrazzo wrote:
> > >
> > > > If you want to be absolutely sure about what the adapter does I
> > > > suggest you to enable statements log on the server and check what
> > > > statements are produced by psycopg. If you find any behaviour
> > > > inconsistent with what documented please let us know.
> > >
> > > One thing I noticed is that it seems pycopg2 does not send a
> > > "set default_transaction_read_only to off" when
> > >
> > > - a database had been created and ALTERed to permanently
> > >   be "default_transaction_read_only to ON"
> > >
> > > - a transaction had been opened on a connection with
> > >
> > >         BEGIN ISOLATION LEVEL SERIALIZABLE READ WRITE
> > >
> > >   in order to run various comments (such as setting
> > >   default client timezone)
> > >
> > > - that transaction had been committed
> > >
> > > - the connection is switched to autocommit=true
> > >     (for running DROP DATABASE et al)
> > >
> > >         2017-08-02 19:18:13 GMT LOG:  00000: Verbindung empfangen: Host=[local]
> > >         2017-08-02 19:18:13 GMT ORT:  BackendInitialize, postmaster.c:4135
> > >         2017-08-02 19:18:13 GMT LOG:  00000: Verbindung autorisiert: Benutzer=postgres Datenbank=gnumed_v20
> > >         2017-08-02 19:18:13 GMT ORT:  PerformAuthentication, postinit.c:272
> > >         2017-08-02 19:18:13 GMT LOG:  00000: statement: BEGIN ISOLATION LEVEL SERIALIZABLE READ WRITE
> > >         2017-08-02 19:18:13 GMT LOCATION:  exec_simple_query, postgres.c:935
> > >         2017-08-02 19:18:13 GMT LOG:  00000: statement: set timezone to 'Europe/Madrid'
> > >         2017-08-02 19:18:13 GMT LOCATION:  exec_simple_query, postgres.c:935
> > >         2017-08-02 19:18:13 GMT LOG:  00000: statement: COMMIT
> > >         2017-08-02 19:18:13 GMT LOCATION:  exec_simple_query, postgres.c:935
> > >         2017-08-02 19:18:13 GMT LOG:  00000: statement: BEGIN ISOLATION LEVEL SERIALIZABLE READ WRITE
> > >         2017-08-02 19:18:13 GMT LOCATION:  exec_simple_query, postgres.c:935
> > >         2017-08-02 19:18:13 GMT LOG:  00000: statement: set lc_messages to 'C'
> > >         2017-08-02 19:18:13 GMT LOCATION:  exec_simple_query, postgres.c:935
> > >         2017-08-02 19:18:13 GMT LOG:  00000: statement: select md5(gm.concat_table_structure(20::integer)) as md5
> > >         2017-08-02 19:18:13 GMT LOCATION:  exec_simple_query, postgres.c:935
> > >         2017-08-02 19:18:14 GMT LOG:  00000: duration: 1156.407 ms
> > >         2017-08-02 19:18:14 GMT LOCATION:  exec_simple_query, postgres.c:1164
> > >         2017-08-02 19:18:14 GMT LOG:  00000: statement: SELECT datname FROM pg_database WHERE
datname='gnumed_v21'
> > >         2017-08-02 19:18:14 GMT LOCATION:  exec_simple_query, postgres.c:935
> > >         2017-08-02 19:18:14 GMT LOG:  00000: statement: COMMIT
> > >         2017-08-02 19:18:14 GMT LOCATION:  exec_simple_query, postgres.c:935
> > >         2017-08-02 19:18:14 GMT LOG:  00000: statement: DROP DATABASE "gnumed_v21"
> > >         2017-08-02 19:18:14 GMT LOCATION:  exec_simple_query, postgres.c:935
> > >         2017-08-02 19:18:14 GMT ERROR:  25006: cannot execute DROP DATABASE in a read-only transaction
> > >         2017-08-02 19:18:14 GMT LOCATION:  PreventCommandIfReadOnly, utility.c:236
> > >         2017-08-02 19:18:14 GMT STATEMENT:  DROP DATABASE "gnumed_v21"
> > >         2017-08-02 19:18:14 GMT LOG:  00000: statement: SET default_transaction_isolation TO DEFAULT
> > >         2017-08-02 19:18:14 GMT LOCATION:  exec_simple_query, postgres.c:935
> > >         2017-08-02 19:18:14 GMT LOG:  00000: statement: SET default_transaction_read_only TO DEFAULT
> > >         2017-08-02 19:18:14 GMT LOCATION:  exec_simple_query, postgres.c:935
> > >         2017-08-02 19:18:14 GMT LOG:  00000: disconnection: session time: 0:00:01.183 user=postgres
database=gnumed_v20host=[local] 
> > >         2017-08-02 19:18:14 GMT LOCATION:  log_disconnections, postgres.c:4501
> > >
> > > The only other indirect proof I have for this is: if I insert
> > > a manual "set default_transaction_read_only to off" right
> > > before the "drop database ..." (but after having been
> > > switched to autocommit) it works as expected.
> > >
> > > If the connection has NOT been used for any other
> > > transactions (that is, if it is switched to autocommit=true
> > > and then to readonly=off) it also works as expected -
> > > psycopg2 sends a "set default_transaction_read_only to off".
> > >
> > > Karsten
> > > --
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> > >
> > >
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