Optimize storing zero page image in WAL as FPI #823
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PG>=16 has optimization for storing zero page in FPI. When storing page as FPIN in WAL records, Postgres excludes page hole (space betweenpd_upper and pd_lower), but it not able to handle zero page (hole size=page size).
It allows to minimize WAL size in case of walloging smgrzeroextend.
PG14/15 doesn't have smgrzeroextend and so has not such optimization.