RE: pg_dumpall and restore

From: Stanton Schmidt <sschmidt@rgllogistics.com>
Sent: Wednesday, October 10, 2018 7:52 AM
To: Rossi, Maria <maria.rossi@jackson.com>
Cc: Laurenz Albe <laurenz.albe@cybertec.at>; pgsql-sql <pgsql-sql@lists.postgresql.org>; pgsql-novice@lists.postgresql.org
Subject: Re: pg_dumpall and restore

When this happened to me the only explanation I could find was that the original table/index had been corrupted.

The only way to "fix" things was to create a copy of the table and insert select distinct * from orig_table.

Hope this helps.

Stanton

From: "Rossi, Maria" <maria.rossi@jackson.com>
To: "Laurenz Albe" <laurenz.albe@cybertec.at>, "pgsql-sql" <pgsql-sql@lists.postgresql.org>, "pgsql-novice@lists.postgresql.org" <pgsql-novice@lists.postgresql.org>
Sent: Tuesday, October 9, 2018 3:05:59 PM
Subject: RE: pg_dumpall and restore

The table  has only 2 columns, name and value.
Select count(*) from table1 at the old database returned 115, on  the  new database, it returned 117.   This a simple select without any WHERE clause.
Thanks.

Maria



-----Original Message-----
From: Laurenz Albe <laurenz.albe@cybertec.at>
Sent: Tuesday, October 9, 2018 2:28 PM
To: Rossi, Maria <maria.rossi@jackson.com>; 'pgsql-sql@lists.postgresql.org' <pgsql-sql@lists.postgresql.org>; 'pgsql-novice@lists.postgresql.org' <pgsql-novice@lists.postgresql.org>
Subject: Re: pg_dumpall and restore

EXTERNAL EMAIL


Rossi, Maria wrote:
> I upgraded our postgres database  from V9.3 to V10.5.  Used pg_dumpall then restore it to the new  instance.
> After the restore, we notice that 1 table had duplicate rows, such that it was not able to create the primary key.
> I checked the old database, it does not have the dups.
> Has anyone encountered  having dups rows  loaded?  Any idea  what caused this and how to prevent?
>  
> Your help would be much appreciated.

I don't believe that pg_dumpall miraculously duplicated the row.

You probably *do* have a duplicate row, and hence table corruption, but I suspect that one of the rows is not in the index you used to look for the row.

If you query:

   SELECT * FROM tab WHERE id = 42;

the query will likely use the index on "id" and find only one of the rows.

You should

   SET enable_indexscan = off;
   SET enable_indexonlyscan = off;

and then repeat the query, so that a sequential scan is used.

To fix, delete one of the rows and reindex.

You can identify a row by its tuple id:

   SELECT ctid, * FROM tab WHERE id = 42;

Yours,
Laurenz Albe
--
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