Find no of extents allocated for a TS

[svij21]

1)What is the query to find the no of extents allocated to a
tablespace.
2) Also how do i find the no of bytes used in the datafile
3)what does USER_BYTES col in DBA_DATA_FILES imply

Just a baby in oracle and so please enlighten my ignorance

[OracleDoc]

Here this will solve questions 1 & 2.

Select t.tablespace_name  "Tablespace",
 t.status "Status",  
 ROUND((MAX(d.bytes)/1024/1024) - (SUM(decode(f.bytes, NULL,0, f.bytes))/1024/1024),2) "Used MB", 
 ROUND(SUM(decode(f.bytes, NULL,0, f.bytes))/1024/1024,2) "Free MB" , 
 t.initial_extent "Initial Extent",   
 t.next_extent "Next Extent",  
 t.min_extents "Min Extents", 
 t.max_extents "Max Extents", 
 t.pct_increase "Pct Increase" 
 , SUBSTR(d.file_name,1,80) "Datafile name" 
FROM DBA_FREE_SPACE f , DBA_DATA_FILES d , DBA_TABLESPACES t 
WHERE t.tablespace_name = d.tablespace_name  
 AND f.tablespace_name(+) = d.tablespace_name  
 AND f.file_id(+) = d.file_id
GROUP BY t.tablespace_name , 
 d.file_name , 
 t.initial_extent ,  
 t.next_extent , 
 t.min_extents , 
 t.max_extents ,  
 t.pct_increase , t.status   
 ORDER BY 1,3 DESC

question 3 you're on your own. I can't answer all of everyones questions, I have a reputation to live up to

[tamilselvan]

The bytes in dba_data_files shows total allocated bytes for a data file.
The user_bytes col shows the total available bytes to be used by segments.

Oracle stores the header info at the beginning of the data file. It uses 8K for DMT, 64K for LMT defined with auto allocate, 1MB for LMT defined with UNIFORM EXTENT size of more than the default value.

The formula is:
Data file header info size = (bytes - user_bytes).

Tamil