Re: [HACKERS] Logical Replication and Character encoding

At Wed, 01 Feb 2017 12:05:40 +0900 (Tokyo Standard Time), Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp> wrote in
<20170201.120540.183393194.horiguchi.kyotaro@lab.ntt.co.jp>
> Hello,
> 
> At Tue, 31 Jan 2017 12:46:18 +0000, "Shinoda, Noriyoshi" <noriyoshi.shinoda@hpe.com> wrote in
<AT5PR84MB0084FAE5976D89CDE9733093EE4A0@AT5PR84MB0084.NAMPRD84.PROD.OUTLOOK.COM>
> >  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?

-- 
Kyotaro Horiguchi
NTT Open Source Software Center
diff --git a/src/backend/replication/logical/proto.c b/src/backend/replication/logical/proto.c
index 1f30de6..3c457a2 100644
--- a/src/backend/replication/logical/proto.c
+++ b/src/backend/replication/logical/proto.c
@@ -16,6 +16,7 @@#include "catalog/pg_namespace.h"#include "catalog/pg_type.h"#include "libpq/pqformat.h"
+#include "mb/pg_wchar.h"#include "replication/logicalproto.h"#include "utils/builtins.h"#include "utils/lsyscache.h"
@@ -442,6 +443,20 @@ logicalrep_write_tuple(StringInfo out, Relation rel, HeapTuple tuple)        pq_sendbyte(out,
't');   /* 'text' data follows */        outputstr = OidOutputFunctionCall(typclass->typoutput, values[i]);
 
+        if (pg_get_client_encoding() != GetDatabaseEncoding())
+        {
+            char *p;
+
+            p = pg_server_to_client(outputstr, strlen(outputstr));
+
+            /* Send the converted string on when succeeded */
+            if (p)
+            {
+                pfree(outputstr);
+                outputstr = p;
+            }
+        }
+        len = strlen(outputstr) + 1;    /* null terminated */        pq_sendint(out, len, 4);        /* length */
 appendBinaryStringInfo(out, outputstr, len); /* data */