pg_buffercache - A lot of "unnamed" relfilenodes?

Hello,

Research on the pg_bufferache showed that a lot of pages don't have any
assigned relfilenodesin pg_class, even when they are dirty (in this case
inserts are done).

SELECT
   relname IS NULL AS relame_is_null,
   isdirty,
   COUNT(*) AS count
FROM
   pg_buffercache b
LEFT OUTER JOIN pg_class c ON b.relfilenode=c.relfilenode
GROUP BY
   relame_is_null,
   isdirty
;

relame_is_null isdirty count
false          false   8914
true           false   7347
true           true    123

Any ideas of this behavior because inserts should have assigned relnames,
shouldn't they?

Thnx.

Ciao,
Gerhard

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