unexpected chunk number 2 (expected 0) for toast value ... inpg_toast_18536

Dear community,

we are seeing the below error on PG 9.6.16 on Debian:

(different issue from the psycopg2 one recently posted by me)

> /home/marc# pg_dump -p 5432 --username=gm-dbo --dbname=gnumed_v22 --compress=0 --no-sync --format=custom
--file=/dev/null
> pg_dump: Ausgabe des Inhalts der Tabelle »doc_obj« fehlgeschlagen: PQgetResult() fehlgeschlagen.
> pg_dump: Fehlermeldung vom Server: ERROR:  unexpected chunk number 2 (expected 0) for toast value 99027 in
pg_toast_18536
> pg_dump: Die Anweisung war: COPY blobs.doc_obj (pk, fk_doc, seq_idx, comment, fk_intended_reviewer, data, filename)
TOstdout; 

    (to note: column "data" is of type BYTEA)

We have been able to identify the row (there may be more)
in blobs.doc_obj which leads to the above error.

    blobs.doc_obj.pk -> 82224

We have ruled out (?) below-PG hardware problems by a
successful run of:

    cp -rv —preserve=all /var/lib/postgresql/9.6  /tmp/

We then tried

    gnumed_v22=# REINDEX TABLE pg_toast.pg_toast_18536;
    REINDEX
    gnumed_v22=# REINDEX TABLE blobs.doc_obj ;
    REINDEX
    gnumed_v22=# VACUUM ANALYZE pg_toast.pg_toast_18536;
    VACUUM
    gnumed_v22=# VACUUM FULL pg_toast.pg_toast_18536;
    VACUUM
    gnumed_v22=# VACUUM ANALYZE blobs.doc_obj ;
    VACUUM
    gnumed_v22=# VACUUM FULL blobs.doc_obj ;
    ERROR:  unexpected chunk number 2 (expected 0) for toast value 99027 in pg_toast_18536

We then tried to DELETE the offending row

    delete from blobs.doc_obj where pk = 82224;

but that, again, shows the "unexpected chunk" problem.

Now, what else can we try to address the problem short of
doing the

    pg_dump --exclude-table-data=blobs.doc_obj

    judicious use of COPY-FROM-with-subselect from blobs.doc_obj

    restore

dance ?

Many thanks,
Karsten
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GPG  40BE 5B0E C98E 1713 AFA6  5BC0 3BEA AC80 7D4F C89B