[dedyoc]

Closes #4294

Rationale for this change

Transaction.table_metadata replays the staged updates on every read:

iceberg-python/pyiceberg/table/__init__.py

Lines 276 to 278 in 718c790

	@property
	def table_metadata(self) -> TableMetadata:
	return update_table_metadata(self._table.metadata, self._updates)

and update_table_metadata always ends in a deep copy:

iceberg-python/pyiceberg/table/update/__init__.py

Line 763 in 718c790

return new_metadata.model_copy(deep=True)

An append reads the property about 20 times before staging anything, so every read deep copies the full snapshot history. This returns the table's metadata directly when nothing is staged, as @geruh suggested on #3302. Table.metadata already shares that object uncopied.

The reproduction script from #4294, on main with and without this change (one timed append per depth):

Snapshots	Before	After	update_table_metadata calls
100	101.3 ms	18.6 ms	22 → 1
200	105.6 ms	27.9 ms	22 → 1
400	245.6 ms	44.6 ms	22 → 1
800	541.5 ms	81.9 ms	22 → 1

Are these changes tested?

Yes. Two tests in tests/table/test_init.py check that with nothing staged the property returns the table's own metadata object and that staged updates are still applied without changing the table's metadata.

test_snapshot_producer_bounded_metadata_access counts update_table_metadata calls as a stand-in for reads of the property, so it now stages an update first, otherwise every read would skip the call. It still fails if a read is added back to the snapshot producer.

Are there any user-facing changes?

No.