I have an application that logs to a DB2 database. Each log is stored in a daily table, meaning that I have several tables, one per each day.
Since the application is running for quite some time, I dropped some of the older daily tables, but the disk space was not reclaimed.
I understand this is normal in DB2, so I goggled and found out that the following command can be used to reclaim space:
db2 alter tablespace <table space> reduce max
Since the tablespace that store the daily log tables is called USERSPACE1, I executed the following command successfully:
db2 alter tablespace userspace1 reduce max
Unfortunately the disk space used by DB2 instance is still the same...
I've read somewhere that the REORG command can be executed, but what I've seen it is used to reorganize tables. Since I dropped the tables, how can I use REORG?
Is there any other way to do this?
Thanks
Reduce the size of a tablespace is very complex. The extents (set of contiguous pages; unit of tablespace allocation) of the tables are not distributed sequentially for a same table. When you reorg a table, the rows will be organized in pages, and the new pages will be written normally at the end of the tablespace. Sometimes, the high watermark will be increased, and your tablespace will be bigger.
You need to reorg all tables from a tablespace in order to "defrag" all tables. Then, you have to perform a new reorg in order to use the previous space, because it should be an empty space in the tablespace.
However, there are many criteria that impacts the organization of the tables in a tablespace: New extents are created (new rows, rows overflow due to updates); compression could be activated after reorg.
What you can do is to assign few or just one table per tablespace; however, you will waste a lot of space (overhead, empty pages, etc.)
The command that you are using is an automatic way to do that, but it does not always work as desired: http://www-01.ibm.com/support/knowledgecenter/SSEPGG_10.5.0/com.ibm.db2.luw.admin.dbobj.doc/doc/c0055392.html
If you want to see the distribution of the tables in your tablespace, you can use db2dart. Then, you can have an idea of which table to reorg (move).
Sorry guys,
The command that I mentioned on the original post works after all, but the space was retrieved very slowly.
Thanks for the help
Related
I have created a table on SQL Server then inserted 135 million records in that table.
then I truncate it
then tried to re-insert the same 135 million records again.
but something went wrong and had to restart the computer
I got the recovery mode in my database.
then fixed.
the problem now is C drive has 10GB free only (210GB used) while before that I used to have 105GB free!
I checked folders but the sum of all sizes including hidden ones does not sum to 210GB
what happened and where did these GBs have gone?
The space is not automatically released by the database. In the case of tempdb, if you restart the sql service, tempdb will reinitialize to original size. But, not the case for other databases.
If you want to reclaim the space, there are two approaches:
Cleaner approch:
As suggested by Paul Randal, go for new filegroup for existing tables and then drop the old filegroup.Refer to his article
Create a new filegroup
Move all affected tables and indexes into the new filegroup using the CREATE INDEX … WITH (DROP_EXISTING = ON) ON syntax, to move the
tables and remove fragmentation from them at the same time
Drop the old filegroup that you were going to shrink anyway (or shrink it way down if its the primary filegroup)
Brute Force approach and redmediation
Here, you can use DBCC SHRINKFILE and reduce the size. Keep little more space in the database to avoid frequent autogrowth. Beware that, shrinking file will lead to index fragmentation and you have to rebuild indexes post the shrinking of files.
As Paul Randal recommends:
If you absolutely have no choice and have to run a data file shrink
operation, be aware that you’re going to cause index fragmentation and
you might need to take steps to remove it afterwards if it’s going to
cause performance problems. The only way to remove index fragmentation
without causing data file growth again is to use DBCC INDEXDEFRAG or
ALTER INDEX … REORGANIZE. These commands only require a single 8KB
page of extra space, instead of needing to build a whole new index in
the case of an index rebuild operation (which will likely cause the
file to grow).
I have a PostgreSQL (10.0 on OS X) database with a single table for the moment. I have noticed something weird when I'm importing a csv file in that table.
When the import fails for various reasons (e.g. one extra row in the csv file or too many characters in a column for a given row), no rows are being added to the table but PostgreSQL still claims that space on my hard disk.
Now, I have a very big csv to import and it failed several time because the csv was not compliant to begin with - so I had tons of import fails that I fixed and tried to import again. What I've realized now is that my computer storage has been reduced by 30-50 GB or so because of that and my database is still empty.
Is that normal?
I suspect this is somewhere in my database cache. Is there a way for me to clear that cache or do I have to fully reinstall my database?
Thanks!
Inserting rows into the database will increase the table size.
Even if the COPY statement fails, the rows that have been inserted so far remain in the table, but they are dead rows since the transaction that inserted them failed.
In PostgreSQL, the SQL statement VACUUM will free that space. That typically does not shrink the table, but it makes the space available for future inserts.
Normally, this is done automatically in the background by the autovacuum daemon.
There are several possibilities:
You disabled autovacuum.
Autovacuum is not fast enough cleaning up the table, so the next load cannot reuse the space yet.
What can you do:
Run VACUUM (VERBOSE) on the table to remove the dead rows manually.
If you want to reduce the table size, run VACUUM (FULL) on the table. That will lock the table for the duration of the operation.
I have a Oracle 11g database with block size = 8192. So, if I'm correct maximum datafile size will be 32GB.
I have a huge table containing around 10 million records. Data in this table will be purged often. For purging we chose CTAS as a better option as we are going to delete greater portion of the data.
As we'll be dropping the old table after CTAS, the old tables are not releasing the space for new tables. I understand that a tablespace has AUTOEXTEND option but no AUTOSHRINK. But the space occupied by old tables should be available for new tables, which is not happening in this case.
I'm getting an Exception saying
ORA-01652: unable to extend temp segment by 8192 in tablespace
FYI the only operation happening all the time is CTAS + Dropping the old table. Nothing else. First time this is working fine, but when the same operation is done the second time, exception arises.
I tried adding an additional datafile to the tablespace, but after few more purge operations on the table, this is also getting full to 32GB and the issue continues.
any script in sql server to find space used by temporary tables + the database name where that temp table was created in tempdb?
The size of my tempDb has grown up to 100 gb and i am not able to recover the space and am unsure what is occupying so much of space.
Thanks for any help.
Temporary tables always gets created in TempDb. However, it is not necessary that size of TempDb is only due to temporary tables. TempDb is used in various ways
Internal objects (Sort & spool, CTE, index rebuild, hash join etc)
User objects (Temporary table, table variables)
Version store (AFTER/INSTEAD OF triggers, MARS)
So, as it is clear that it is being use in various SQL operations so size can grow due to other reasons also
You can check what is causing TempDb to grow its size with below query
SELECT
SUM (user_object_reserved_page_count)*8 as usr_obj_kb,
SUM (internal_object_reserved_page_count)*8 as internal_obj_kb,
SUM (version_store_reserved_page_count)*8 as version_store_kb,
SUM (unallocated_extent_page_count)*8 as freespace_kb,
SUM (mixed_extent_page_count)*8 as mixedextent_kb
FROM sys.dm_db_file_space_usage
if above query shows,
Higher number of user objects then it means that there is more usage of Temp tables , cursors or temp variables
Higher number of internal objects indicates that Query plan is using a lot of database. Ex: sorting, Group by etc.
Higher number of version stores shows Long running transaction or high transaction throughput
based on that you can configure TempDb file size. I've written an article recently about TempDB configuration best practices. You can read that here
Perhaps you can use following SQL command on temp db files seperately
DBCC SHRINKFILE
Please refer to https://support.microsoft.com/en-us/kb/307487 for more information
I'm trying to convert the permanent tables used in a stored procedure to global temp tables. I've looked at the stats on these permanent tables and some have tens of millions of rows of data and are on the order if gigabytes in size (up to 10 GB).
So,
CREATE TABLE my_table (
column1 NUMBER,
column2 NUMBER,
etc...
)
TABLESPACE BIGTABLESPACE
NOLOGGING
NOCOMPRESS
NOCACHE
NOPARALLEL
MONITORING;
should become
CREATE GLOBAL TEMPORARY TABLE my_table (
column1 NUMBER,
column2 NUMBER,
etc..
)
ON COMMIT PRESERVE ROWS;
I'm creating an equivalent global temporary table with rows that should be preserved until the end of the session for each existing permanent table. This global temp table will be used in the procedure instead of the permanent table.
(EXECUTE IMMEDIATE 'TRUNCATE ...' at the start, and INSERT /*+ APPEND */ INTO at some later point)
All of the permanent tables have been created in a big tablespace BIGTABLESPACE
The Oracle docs state that the global temporary table will be created in the user's temp tablespace (I assume this is TEMP). The problem with this is that the TEMP tablespace is small and the extents are not set to grow to the size I need them to grow during the procedure.
The TEMP tablespace was created during the database creation
create database "$oracle\_sid"
user sys identified by "$sys\_password"
user system identified by "$system\_password"
set default bigfile tablespace
controlfile reuse
maxdatafiles 256
maxinstances $maxinstances
maxlogfiles 16
maxlogmembers 3
maxloghistory 1600
noarchivelog
character set WE8MSWIN1252
national character set AL16UTF16
datafile
'$oracle\_home/oradata/$oracle\_sid/system01.dbf' size 512M
logfile
'$oracle\_home/oradata/$oracle\_sid/redo01.log' size 1G,
'$oracle\_home/oradata/$oracle\_sid/redo02.log' size 1G,
'$oracle\_home/oradata/$oracle\_sid/redo03.log' size 1G
sysaux datafile
'$oracle\_home/oradata/$oracle\_sid/sysaux01.dbf' size 256M
default temporary tablespace temp tempfile
'$oracle\_home/oradata/$oracle\_sid/temp01.dbf' size 5G
undo tablespace "UNDOTBS1" datafile
'$oracle\_home/oradata/$oracle\_sid/undotbs01.dbf' size 5G;
The permanent tables (that I'm planning to replace) were originally created in tablespace BIGTABLESPACE
-- 50G bigfile datafile size
create bigfile tablespace "BIGTABLESPACE"
datafile '$oracle\_home/oradata/$oracle\_sid/bts01.dbf' size 50G
extent management local
segment space management auto;
The permanent table indexes were originally created in tablespace BIGTABLESPACE
-- 20G bigfile datafile size
create bigfile tablespace "BIGINDXSPACE"
datafile '$oracle\_home/oradata/$oracle\_sid/btsindx01.dbf' size 20G
extent management local
segment space management auto;
Is replacing these permanent tables with global temporary tables feasable?
The TEMP tablespace will run into a problem extending the TEMP tablespace. Is there a way to create global temporary tables and their indexes in tablespaces BIGTABLESPACE and BIGINDXSPACE?
If not, how can I make the TEMP tablespace behave like a bigfile tablespace and achieve index/table separation?
Can I create two TEMP bigfile tablespaces and create indexes into one and tables into another?
I want to use global temporary tables, but the volume of data I am handling in the procedure would seem to be above and beyond the indended design of global temporary tables.
Any suggestions?
There is no benefit to separating data and indexes into separate tablespaces other than potentially making DBAs more comfortable that similar objects are grouped together. There is a long-standing myth that separating indexes and data was beneficial for performance reasons-- that is not correct.
Temporary objects should (and must) be stored in a temporary tablespace. You could increase the size of your TEMP tablespace or create a separate temporary tablespace just for the user(s) that will own these objects if you wanted to segregate these large temporary tables into a separate tablespace. You can't (and wouldn't want to) store them in your permanent tablespaces.
Architecturally, though, I would be very curious about why temporary tables were necessary in your system. If you have sessions that are writing 10's of GB into temporary tables, then presumably reading those 10's of GB out again in order to write the data somewhere else, I would tend to suspect that there were more efficient solutions. It is very rare in Oracle to even need temporary tables-- it is far more common in other databases where readers can block writers to need to copy data out of tables before working on it. Oracle has no such limitations.
I don't think that there's anything in your description that makes GTT's unattractive. You obviously need very large temporary tablespaces but you're not consuming more space overall unless you've been making heavy use of table compression (unavailable in GTT's at least up to 10gR2). Look into the use of tablespace groups: http://download.oracle.com/docs/cd/B19306_01/server.102/b14231/tspaces.htm#ADMIN01103
Using a tablespace group, rather than a single temporary tablespace, can alleviate problems caused where one tablespace is inadequate to hold the results of a sort, particularly on a table that has many partitions. A tablespace group enables parallel execution servers in a single parallel operation to use multiple temporary tablespaces.
Also, don't neglect the use of subquery factoring clauses. They can often replace the use of temporary tables. However they might still require just as much temporary storage space because a large result set from a SQFC can spill to disk to avoid the consumption of too much memory, so you still have to go ahead with the increase in TEMP space. They're very handy for not having to deploy a new database object every time you need a new temporary table.
I looked at large sized Global Temporary Tables for a migration exercise. It worked but for debugging and rejection hadling I eventually went with plain tables.
If the GTTs don't work out, consider either Row-Level Security / VPD (or even views).
You can have a column derived from sys_context('USERENV','SESSIONID') and use that to ensure that the user can only see their own data.
Still the thought of multiple sessions dealing with multi-gigabyte datasets concurrently is a bit scary.
PS. I believe that for GTTs used through a procedure use the temp tablespace of the session user rather than the temp tablespace of the procedure owner. If you can get the sessions as separate oracle users then you have a chance at spreading your file IO over different tablespaces.