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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