CHECKPOINT_TIME column in V$DATAFILE

Question

Hello,
What really CHECKPOINT_TIME column mean in v$datafile. I understand that when SCN occurrs a checkpoint is recorded. Does this time represent the time when DBWR launches the write process on datafiles?
Pleaes concur or conquer.
R

Answer 1

I thought aggregating bytes from v$datafile would give me accurate info. I was basing it from following link where it says v$datafile holds current size.
http://download.oracle.com/docs/cd/B12037_01/server.101/b10755/dynviews_1057.htm#sthref3063
If above is still not correct and like you said, it holds empty space allocated then I would have to use below mentioned query, but my first preference is v$datafile because of its simplicity.
SELECT x$index_history.tablespace_name, x$index_history.owner,
x$index_history.index_name,
x$index_history.clustering_factor,
x$index_history.leaf_blocks, x$index_history.blevel,
y$segment_index.next_extent, y$segment_index.extents,
y$segment_index.segment_type,
y$segment_index.BYTES index_bytes,
e$table_history.tablespace_name table_space_name,
e$table_history.owner table_owner,
e$table_history.table_name,
z$segment_table.next_extent table_next_extent,
z$segment_table.extents table_extents,
z$segment_table.segment_type segmentt_type,
z$segment_table.BYTES table_bytes, SYSDATE
FROM dba_indexes x$index_history,
dba_segments y$segment_index,
dba_segments z$segment_table,
dba_tables e$table_history
WHERE x$index_history.table_name = e$table_history.table_name
AND y$segment_index.segment_name = x$index_history.index_name
AND y$segment_index.tablespace_name =
x$index_history.tablespace_name
AND y$segment_index.owner = x$index_history.owner
AND y$segment_index.segment_type = 'INDEX'
AND x$index_history.owner NOT IN ('SYS', 'SYSTEM')
AND z$segment_table.segment_name = e$table_history.table_name
AND z$segment_table.tablespace_name =
e$table_history.tablespace_name
AND z$segment_table.owner = e$table_history.owner
AND z$segment_table.segment_type = 'TABLE'
AND e$table_history.owner NOT IN ('SYS', 'SYSTEM')
AND e$table_history.num_rows > 500000;
Thanks,
Rich