Oracle not reuse deleted blocks - oracle

Question

I'm trying to insert data from PURCHASE_HIST_D to PURCHASE_HIST.
(different schemas in different servers, with DBLINK).
The target table has a lot of deleted data blocks.
This is how I'm checking the segments vs the used blocks:
-- result : 199.8743480481207370758056640625 GB
select (AVG_ROW_LEN*NUM_ROWS)/1024/1024/1024 from DBA_TABLES where TABLE_NAME='PURCHASE_HIST';
-- result: 250.7939453125 GB
select SUM(BYTES)/1024/1024/1024 from DBA_SEGMENTS where SEGMENT_NAME='PURCHASE_HIST';
which means that there are 50 GB of used blocks which can be reuse for the new data.
I'm query the same for the source table:
-- result: 21.8079682849347591400146484375
select (AVG_ROW_LEN*NUM_ROWS)/1024/1024/1024 from DBA_TABLES where TABLE_NAME='PURCHASE_HIST_D';
-- result: 27.447265625
select SUM(BYTES)/1024/1024/1024 from DBA_SEGMENTS where SEGMENT_NAME='PURCHASE_HIST_D';
The source is only 27 GB so It's looks like I dont need to add more space for the tablespace.
This is the free tablespace information:
-- result: 1889477 (Used MB) 4923 (Free MB) 1894400 (Total MB)
select
fs.tablespace_name "Tablespace",
(df.totalspace - fs.freespace) "Used MB",
fs.freespace "Free MB",
df.totalspace "Total MB",
round(100 * (fs.freespace / df.totalspace)) "Pct. Free"
from
(select
tablespace_name,
round(sum(bytes) / 1048576) TotalSpace
from
dba_data_files
group by
tablespace_name
) df,
(select
tablespace_name,
round(sum(bytes) / 1048576) FreeSpace
from
dba_free_space
group by
tablespace_name
) fs
WHERE
DF.TABLESPACE_NAME = FS.TABLESPACE_NAME
and df.TABLESPACE_NAME = 'TS_DWHDATA';
So why when I'm execute the insert (even with NOAPPEND hint) I get an error that there is no enough space in tablesapce?
-- examole of the Insert
INSERT
/*+ monitor NOAPPEND parallel(64) statement_queuing */
INTO DWH.PURCHASE_HIST
SELECT *
FROM DWH_MIG.PURCHASE_HIST_D#DWH_MIG ;
The exception:
ORA-01653: unable to extend table DWH.PURCHASE_HIST by 8192 in tablespace TS_DWHDATA

Answer 1

You are getting the free space (using query) from the table but the high watermark is still at the point from where you can not insert data below that.
You need to reclaim that space using the following:
alter table your_table enable row movement;
alter table your_table shrink space cascade;
Also, You will need to rebuild the indexes of the table after such an operation.
Refer Oracle documentation for reclaiming waste space.
Cheers!!