Re: Logical Replication and Character encoding

Hello.

This version makes subscriber automatically set its database
encoding to clinet_encoding (if not explicitly set). And changed
the behavior when pg_server_to_client returns NULL to ERROR from
sending original string.

At Wed, 1 Feb 2017 08:39:41 +0000, "Shinoda, Noriyoshi" <noriyoshi(dot)shinoda(at)hpe(dot)com> wrote in <AT5PR84MB0084A18D3BF1D93B862E95E4EE4D0(at)AT5PR84MB0084(dot)NAMPRD84(dot)PROD(dot)OUTLOOK(dot)COM>
> Thank you for creating patches.
> I strongly hope that your patch will be merged into the new
> version. Since all databases are not yet based on UTF - 8, I
> think conversion of character codes is still necessary.

Thanks.

> -----Original Message-----
> From: Kyotaro HORIGUCHI [mailto:horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp]
> Sent: Wednesday, February 01, 2017 3:31 PM
> To: Shinoda, Noriyoshi <noriyoshi(dot)shinoda(at)hpe(dot)com>
> Cc: pgsql-hackers(at)postgresql(dot)org
> Subject: Re: [HACKERS] Logical Replication and Character encoding
>
> At Wed, 01 Feb 2017 12:13:04 +0900 (Tokyo Standard Time), Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp> wrote in <20170201(dot)121304(dot)267734380(dot)horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>
> > > > I tried a committed Logical Replication environment. I found
> > > > that replication between databases of different encodings did not
> > > > convert encodings in character type columns. Is this behavior
> > > > correct?
> > >
> > > The output plugin for subscription is pgoutput and it currently
> > > doesn't consider encoding but would easiliy be added if desired
> > > encoding is informed.
> > >
> > > The easiest (but somewhat seems fragile) way I can guess is,
> > >
> > > - Subscriber connects with client_encoding specification and the
> > > output plugin pgoutput decide whether it accepts the encoding
> > > or not. If the subscriber doesn't, pgoutput send data without
> > > conversion.
> > >
> > > The attached small patch does this and works with the following
> > > CREATE SUBSCRIPTION.
> >
> > Oops. It forgets to care conversion failure. It is amended in the
> > attached patch.
> >
> > > CREATE SUBSCRIPTION sub1 CONNECTION 'host=/tmp port=5432
> > > dbname=postgres client_encoding=EUC_JP' PUBLICATION pub1;
> > >
> > >
> > > Also we may have explicit negotiation on, for example,
> > > CREATE_REPLICATION_SLOT.
> > >
> > > 'CREATE_REPLICATION_SLOT sub1 LOGICAL pgoutput ENCODING EUC_JP'
> > >
> > > Or output plugin may take options.
> > >
> > > 'CREATE_REPLICATION_SLOT sub1 LOGICAL pgoutput OPTIONS(encoding EUC_JP)'
> > >
> > >
> > > Any opinions?
>
> This patch chokes replication when the publisher finds an inconvertible character in a tuple to be sent. For the case, dropping-then-recreating subscription is necessary to go forward.

I think this behavior is right and inevitable in order to protect
subscribers from broken strings.

regards,

--
Kyotaro Horiguchi
NTT Open Source Software Center