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  1. Don't trust deferred-unique indexes for join removal.

  1. Unreproducible bug in snapshot import code

    Gurjeet Singh <singh.gurjeet@gmail.com> — 2011-10-24T16:55:44Z

    Hi All,

    I have not been able to reproduce this error, but wanted to report this
in case it might be useful.

    Commit -id: 0f39d5050dc0dce99258381f33f1832c437aff85

    Configure options:
    --prefix=/mnt/storage/gurjeet/dev/builds//master/db --enable-debug
--enable-cassert CFLAGS=-O0 --enable-depend --enable-thread-safety
--with-openssl

    Used VPATH to build postgres.

    Attached files: terminal1.txt termonal2.txt config.log

    Starting from line 89 of terminal1.txt we see this snippet:

postgres=# rollback;
ROLLBACK
postgres=# begin TRANSACTION ;
BEGIN
postgres=# set transaction snapshot '000002C8-1';
ERROR:  SET TRANSACTION SNAPSHOT must be called before any query
postgres=# rollback;
ROLLBACK


    As you can see the SET TRANSACTION SNAPSHOT was the first statement in
that transaction, and yet the ERROR message says that it is not. That
snapshot id was generated in another session (terminal2.txt), and was
generated outside any transaction; that's the only peculiar thing I can say
about that snapshot-id.

    As is evident from the rest of the lines in terminal1.txt, I have not
been able to reproduce this error again; I tried even with a clean build of
the sources.

    I have taken a look at the code and everything tells me that the error
should have been:

ERROR:  a snapshot-importing transaction must have isolation level
SERIALIZABLE or REPEATABLE READ

    Maybe it was not a clean build the first time, and the code may have
wrongly linked with previously compiled .o files.

Regards,
-- 
Gurjeet Singh
EnterpriseDB Corporation
The Enterprise PostgreSQL Company

  2. Re: Unreproducible bug in snapshot import code

    Tom Lane <tgl@sss.pgh.pa.us> — 2011-10-24T17:05:55Z

    Gurjeet Singh <singh.gurjeet@gmail.com> writes:
>     Starting from line 89 of terminal1.txt we see this snippet:

> postgres=# rollback;
> ROLLBACK
> postgres=# begin TRANSACTION ;
> BEGIN
> postgres=# set transaction snapshot '000002C8-1';
> ERROR:  SET TRANSACTION SNAPSHOT must be called before any query
> postgres=# rollback;
> ROLLBACK

>     As is evident from the rest of the lines in terminal1.txt, I have not
> been able to reproduce this error again; I tried even with a clean build of
> the sources.

Given the weird capitalization of the BEGIN command, I'm guessing that
you used tab-completion to enter it.  I wonder if this could have been
affected by the execution of some query in support of tab completion?
I couldn't reproduce it either on the basis of that guess, though.

			regards, tom lane

  3. Re: Unreproducible bug in snapshot import code

    Alvaro Herrera <alvherre@commandprompt.com> — 2011-10-24T17:08:30Z

    Excerpts from Gurjeet Singh's message of lun oct 24 13:55:44 -0300 2011:

>     Starting from line 89 of terminal1.txt we see this snippet:
> 
> postgres=# rollback;
> ROLLBACK
> postgres=# begin TRANSACTION ;
> BEGIN
> postgres=# set transaction snapshot '000002C8-1';
> ERROR:  SET TRANSACTION SNAPSHOT must be called before any query
> postgres=# rollback;
> ROLLBACK
> 
> 
>     As you can see the SET TRANSACTION SNAPSHOT was the first statement in
> that transaction, and yet the ERROR message says that it is not.

Maybe the tab-completion feature issued a query before the set
transaction command.

-- 
Álvaro Herrera <alvherre@commandprompt.com>
The PostgreSQL Company - Command Prompt, Inc.
PostgreSQL Replication, Consulting, Custom Development, 24x7 support

  4. Re: Unreproducible bug in snapshot import code

    Gurjeet Singh <singh.gurjeet@gmail.com> — 2011-10-24T17:41:34Z

    On Mon, Oct 24, 2011 at 1:08 PM, Alvaro Herrera
<alvherre@commandprompt.com>wrote:

>
> Excerpts from Gurjeet Singh's message of lun oct 24 13:55:44 -0300 2011:
>
> >     Starting from line 89 of terminal1.txt we see this snippet:
> >
> > postgres=# rollback;
> > ROLLBACK
> > postgres=# begin TRANSACTION ;
> > BEGIN
> > postgres=# set transaction snapshot '000002C8-1';
> > ERROR:  SET TRANSACTION SNAPSHOT must be called before any query
> > postgres=# rollback;
> > ROLLBACK
> >
> >
> >     As you can see the SET TRANSACTION SNAPSHOT was the first statement
> in
> > that transaction, and yet the ERROR message says that it is not.
>
> Maybe the tab-completion feature issued a query before the set
> transaction command.
>

I have tried reproducing the bug starting from 1 and 2 transactions before
the one shown in snippet, and I used tab-completion to get the same
screen-output as termonal1.txt and yet it's not reproducible.

Regards,
-- 
Gurjeet Singh
EnterpriseDB Corporation
The Enterprise PostgreSQL Company

  5. Re: Unreproducible bug in snapshot import code

    Fujii Masao <masao.fujii@gmail.com> — 2011-10-25T06:33:41Z

    On Tue, Oct 25, 2011 at 2:41 AM, Gurjeet Singh <singh.gurjeet@gmail.com> wrote:
> On Mon, Oct 24, 2011 at 1:08 PM, Alvaro Herrera <alvherre@commandprompt.com>
> wrote:
>>
>> Excerpts from Gurjeet Singh's message of lun oct 24 13:55:44 -0300 2011:
>>
>> >     Starting from line 89 of terminal1.txt we see this snippet:
>> >
>> > postgres=# rollback;
>> > ROLLBACK
>> > postgres=# begin TRANSACTION ;
>> > BEGIN
>> > postgres=# set transaction snapshot '000002C8-1';
>> > ERROR:  SET TRANSACTION SNAPSHOT must be called before any query
>> > postgres=# rollback;
>> > ROLLBACK
>> >
>> >
>> >     As you can see the SET TRANSACTION SNAPSHOT was the first statement
>> > in
>> > that transaction, and yet the ERROR message says that it is not.
>>
>> Maybe the tab-completion feature issued a query before the set
>> transaction command.
>
> I have tried reproducing the bug starting from 1 and 2 transactions before
> the one shown in snippet, and I used tab-completion to get the same
> screen-output as termonal1.txt and yet it's not reproducible.

I could reproduce it when I typed TAB just after typing "set" in "set
transaction snapshot".
As Tom and Alvaro pointed out, the tab-completion issues a query and which
prevents the "set transaction snapshot" command.

Regards,

-- 
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center

  6. Re: Unreproducible bug in snapshot import code

    Gurjeet Singh <singh.gurjeet@gmail.com> — 2011-10-25T13:54:08Z

    On Tue, Oct 25, 2011 at 2:33 AM, Fujii Masao <masao.fujii@gmail.com> wrote:

> On Tue, Oct 25, 2011 at 2:41 AM, Gurjeet Singh <singh.gurjeet@gmail.com>
> wrote:
> > On Mon, Oct 24, 2011 at 1:08 PM, Alvaro Herrera <
> alvherre@commandprompt.com>
> > wrote:
> >>
> >> Excerpts from Gurjeet Singh's message of lun oct 24 13:55:44 -0300 2011
> :
> >>
> >> >     Starting from line 89 of terminal1.txt we see this snippet:
> >> >
> >> > postgres=# rollback;
> >> > ROLLBACK
> >> > postgres=# begin TRANSACTION ;
> >> > BEGIN
> >> > postgres=# set transaction snapshot '000002C8-1';
> >> > ERROR:  SET TRANSACTION SNAPSHOT must be called before any query
> >> > postgres=# rollback;
> >> > ROLLBACK
> >> >
> >> >
> >> >     As you can see the SET TRANSACTION SNAPSHOT was the first
> statement
> >> > in
> >> > that transaction, and yet the ERROR message says that it is not.
> >>
> >> Maybe the tab-completion feature issued a query before the set
> >> transaction command.
> >
> > I have tried reproducing the bug starting from 1 and 2 transactions
> before
> > the one shown in snippet, and I used tab-completion to get the same
> > screen-output as termonal1.txt and yet it's not reproducible.
>
> I could reproduce it when I typed TAB just after typing "set" in "set
> transaction snapshot".
> As Tom and Alvaro pointed out, the tab-completion issues a query and which
> prevents the "set transaction snapshot" command.
>

Great! That settles it then. Reproducible, but not a bug.

Thanks,
-- 
Gurjeet Singh
EnterpriseDB Corporation
The Enterprise PostgreSQL Company

  7. Re: Unreproducible bug in snapshot import code

    Bruce Momjian <bruce@momjian.us> — 2011-10-28T14:11:09Z

    Gurjeet Singh wrote:
> > > I have tried reproducing the bug starting from 1 and 2 transactions
> > before
> > > the one shown in snippet, and I used tab-completion to get the same
> > > screen-output as termonal1.txt and yet it's not reproducible.
> >
> > I could reproduce it when I typed TAB just after typing "set" in "set
> > transaction snapshot".
> > As Tom and Alvaro pointed out, the tab-completion issues a query and which
> > prevents the "set transaction snapshot" command.
> >
> 
> Great! That settles it then. Reproducible, but not a bug.

Yes, it is only tabs that query the database for completion that cause
this.  Should this be documented somehow?  (No idea how.)

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + It's impossible for everything to be true. +

  8. Re: Unreproducible bug in snapshot import code

    Gurjeet Singh <singh.gurjeet@gmail.com> — 2011-10-28T15:07:25Z

    On Fri, Oct 28, 2011 at 10:11 AM, Bruce Momjian <bruce@momjian.us> wrote:

> Gurjeet Singh wrote:
> > > > I have tried reproducing the bug starting from 1 and 2 transactions
> > > before
> > > > the one shown in snippet, and I used tab-completion to get the same
> > > > screen-output as termonal1.txt and yet it's not reproducible.
> > >
> > > I could reproduce it when I typed TAB just after typing "set" in "set
> > > transaction snapshot".
> > > As Tom and Alvaro pointed out, the tab-completion issues a query and
> which
> > > prevents the "set transaction snapshot" command.
> > >
> >
> > Great! That settles it then. Reproducible, but not a bug.
>
> Yes, it is only tabs that query the database for completion that cause
> this.  Should this be documented somehow?  (No idea how.)
>

If we have a doc section on psql's tab-completion, I think this needs to go
there. A note like:

"Trying to tab-complete on psql may send queries to the server, and
depending on the transaction state, execution of these queries may lead to
non-default/unexpected behaviour by the queries executed after
tab-completion. For example, ..."

Regards,
-- 
Gurjeet Singh
EnterpriseDB Corporation
The Enterprise PostgreSQL Company

  9. Re: Unreproducible bug in snapshot import code

    Bruce Momjian <bruce@momjian.us> — 2012-08-16T22:44:45Z

    On Fri, Oct 28, 2011 at 11:07:25AM -0400, Gurjeet Singh wrote:
> On Fri, Oct 28, 2011 at 10:11 AM, Bruce Momjian <bruce@momjian.us> wrote:
> 
>     Gurjeet Singh wrote:
>     > > > I have tried reproducing the bug starting from 1 and 2 transactions
>     > > before
>     > > > the one shown in snippet, and I used tab-completion to get the same
>     > > > screen-output as termonal1.txt and yet it's not reproducible.
>     > >
>     > > I could reproduce it when I typed TAB just after typing "set" in "set
>     > > transaction snapshot".
>     > > As Tom and Alvaro pointed out, the tab-completion issues a query and
>     which
>     > > prevents the "set transaction snapshot" command.
>     > >
>     >
>     > Great! That settles it then. Reproducible, but not a bug.
> 
>     Yes, it is only tabs that query the database for completion that cause
>     this.  Should this be documented somehow?  (No idea how.)
> 
> 
> If we have a doc section on psql's tab-completion, I think this needs to go
> there. A note like:
> 
> "Trying to tab-complete on psql may send queries to the server, and depending
> on the transaction state, execution of these queries may lead to non-default/
> unexpected behaviour by the queries executed after tab-completion. For example,
> ..."

I have added the attached patch to document this limitation.

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + It's impossible for everything to be true. +