I have been playing with Apex for an internal application Application Express is a great tool, and Oracle has an internal Apex environment that groups can use for their own internal applications.
In creating the application I learned how to do a Javascript window that pops up within a page to help enter data. This can be very useful to add a function to your application without adding more pages.
This is how its down..
First I created a table to contain breweries.. Since this is running on 12.1, I was able to use the new feature to automagically use a sequence as a default value (it's about time right) ?
Here is my table creation script..
CREATE SEQUENCE brewery_seq
START WITH 1000
INCREMENT BY 1
NOCACHE
NOCYCLE;
I often get questions around the FRA (Flash Recovery Area), and how it should be used when moving backups to the ZDLRA.
First though, the recommendation is to ALWAYS set your db_recovery_file_dest_size to be 10% less than the amount of space available, and don't put other files in this same location (that are not managed as part of the FRA).
Having a 10% buffer ensures that you can increase the available storage if necessary. For those experienced on-call DBA's I'm sure there have been times where increasing the db_recovery_file_dest_size by that last 10% was used to keep the database running while space was cleaned up.. And of course this is often at 3:00 AM when the dreaded "archive log destination full" alert comes across.
First let's go through what's in the FRA and how it's being used.
There is a lot of information in MOS and I will include pertinent MOS notes at the end of this post.
What's in the FRA (V$FLASH_RECOVERY_AREA_USAGE shows us )?
Here is a sample output SQL> Select file_type, percent_space_used as used, percent_space_reclaimable as reclaimable, number_of_files as "number" from v$flash_recovery_area_usage; FILE_TYPE USED RECLAIMABLE number ------------ ---------- ----------- ---------- CONTROLFILE 0 0 0 ONLINELOG 0 0 0 ARCHIVELOG 4.77 0 2 BACKUPPIECE 56.80 0 10 IMAGECOPY 0 0 0 FLASHBACKLOG 11.68 11.49 63 From this you can see the following items are in the FRA. CONTROLFILE -- This comes from setting the location of the CONTROLFILE backup. configure controlfile autobackup on; If you configure controlfile backups using the 'FORMAT" option, it will not be managed by the FRA. ONLINELOG A copy of the online redo logs go to the FRA when the DB_RECOVERY_FILE_DEST is set and the DB_CREATE_ONLINE_LOG_DEST_n is not set.
ARCHIVELOG -- Archive logs are managed by the FRA when the archive LOG_ARCHIVE_DEST_n parameter contains the clause 'LOCATION=USE_DB_RECOVERY_FILE_DEST'
alter system set LOG_ARCHIVE_DEST_1='LOCATION=USE_DB_RECOVERY_FILE_DEST'';
BACKUPPIECE or IMAGECOPY
RMAN backups are managed by the FRA when you configure RMAN to (or explicitly) send backups to disk AND the FORMAT option is not specified.
FLASHBACKLOG
If flashback database is turned on for the database, flashback logs will be kept in the FRA automatically. The database parameter db_flashback_retention_target is set to determine the amount of flashback logs that are kept for the database.
Now let's take a look at how space is managed for each piece
ONLINELOG -- Since online redo logs are necessary for the database, this is not affected with space pressure.
FLASHBACKLOG -- Flashback logs are automatically removed to keep the window specified in the DB_FLASHBACK_RETENTION_TARGET setting. If there is space pressure, the flashback management will automatically release space until it hits a window of 1 hour. This is the default and comes from the _MINIMUM_DB_FLASHBACK_RETENTIONparameter. BACKUPPIECE or IMAGECOPY and/or CONTROLFILE and ARCHIVELOG -- these are managed by the setting in RMAN for the retention policy.
The recommendation for the ZDLRA (when using real-time redo apply) is to set this parameter to
CONFIGURE ARCHIVELOG RETENTION POLICY SHIPPED to all STANDBY;
NOTE - This policy marks archive logs as "reclaimable" as soon as they are considered shipped to ALL standby databases. If the ZDLRA is the only external destination, then as soon as it's received on the ZDLRA, it is "reclaimable". If you have Dataguard along with ZDLRA, then archive logs are considered "reclaimable" as soon as they are received by both. OR CONFIGURE ARCHIVELOG RETENTION POLICY APPLIED on all STANDBY; NOTE - This policy marks archive logs as "reclaimable" as soon as they are considered APPLIED on ALL standby databases. If the ZDLRA is the only external destination, then as soon as it's received on the ZDLRA AND has been cataloged, it is "reclaimable". This takes less than a minute, and occurs independent of the protected database. If you have Dataguard along with ZDLRA, then archive logs are considered "reclaimable" as soon as they are applied by both. *** Note that "APPLIED" is the most desirable because this ensures that the log is not removed until it "processed" by all destinations, HOWEVER, if you have a standby location that has a gap in apply then you need to consider "SHIPPED". Both Policies will work, but it depends on your configuration.
The recommendation for the ZDLRA (when using log sweeps) is to set this parameter to
CONFIGURE ARCHIVELOG RETENTION POLICY xx backed up 1 times device type SBT; Where XXX is 1) not used if there is no Dataguard or other destinations beyond local disk for archive logs. 2) "SHIPPED to all STANDBY" if Dataguard or Golden Gate is used. 3) "APPLIED" on all STANDBY if Dataguard or Golden Gate is used.
Now let's take a look at how space is managed (315098.1) There is a MOS note on this, but it there are still some misconceptions on what you see happening. Looking at the output of view V$RECOVERY_FILE_DEST you will see 3 pertinent columns. SPACE_LIMIT ==> this is the amount of space that is allocated to the FRA. SPACE_USED ==> This is the amount of space currently used SPACE_RECLAIMABLE ==> This is the amount space that the FRA considers reclaimable. ** This NOT the total amount space reclaimable, just the amount that the FRA knows about (I'll get to what this means soon). The note says that If the free space becomes less then 15% in
the Flash Recovery Area then all the archivelogs in the Flash Recovery Area which are not needed for
recovery by the current backups in the FRA will become obsolete and the space
occupied will be shown in the SPACE RECLAIMABLE
column of V$RECOVERY_FILE_DEST.
From this I made some assumptions that were incorrect.
I assumed
1) Since I was immediately sending all backups and archive logs to the ZDLRA (Real Time Apply), the space for the ARCHIVELOG would all show up in the SPACE_RECLAIMABLE column.
2) When the FRA reaches 85%, it would automatically clean up ARCHIVELOGS to bring it down to 85%.
Both of these assumptions were wrong. By testing I found that this is what actually happens, and this still falls within the verbiage in that note.
This is what happens as the space fills up. For my example I have a 1 TB FRA.
849 GB used in the FRA. The reclaimable space is NOT calculated yet because we have not hit the 85% full mark.
Space_limit 1000GB
Space_used 849GB
Space_reclaimable 0GB
At 850GB I reached 85% full. This is the point where the database calculates SPACE_RECLAIMABLE. Note that it does not fully calculate what's reclaimable, it only finds a portion of the reclaimable space.
Space_limit 1000GB
Space_used 850GB
Space_reclaimable 300GB
At 999GB it's not quite full. The reclaimable space shows there is space available,
but it still only finds a portion of the available space.
Space_limit 1000GB
Space_used 999GB
Space_reclaimable 300GB
At 1000GB it is completely full. The reclaimable space shows space available to be reclaimed.
At this point I can see in the alert log that archive logs are being removed.
Only enough logs are removed to make space for new logs. it remains at 99% used.
Space_limit 1000GB
Space_used 999GB
Space_reclaimable 160GB
As I added more logs, it remained at 99% used.
This makes it very difficult to know how much space you have available in your FRA.
The warnings start occurring at the 85% full mark.
Since the FRA recalculates the SPACE_RECLAIMABLE at 85% full, but only adjusts it to keep from warning,
it is impossible to tell how much TOTAL space is reclaimable.
Using the formula
SPACE_LIMIT - SPACE_RECLAIMABLE
Does not give you amount of space that is actually reclaimable.
It is only useful to tell you when the amount of unreclaimable space > 85%.
Here are the useful MOS notes.
NOTE:305817.1 - FAQ - Flash Recovery Area feature
How is the space pressure managed in the Flash Recovery Area - An Example. (Doc ID 315098.1)
Correctly configuring the Flash Recovery Area to allow the release of reclaimable space (Doc ID 316074.1)
I wanted to write a post on one of Oracle's newest products (Well not that new).. The ZDLRA.
The ZDLRA is often referred to as "Zelda". I know the name ZDLRA does not roll off the tongue well. Zelda is a much better (and easier to say name).
The other name you will hear the ZDLRA referred to as is RA or Recover Appliance.
Recover Appliance is probably the best description of the product. One of the things that makes this product unique is the emphasis on RECOVERY.. Notice there is not a mention of backup in the name.
It does a lot of it's magic by using incremental forevers --
I know what you are thinking... The incremental forever strategy has been around for a long time (since 10.2 I think). The idea is simple. You take a full backup (database copy NOT backup set), and then take incrementals from then on. You use RMAN to apply the incremental to the full, and create a new full (destroying the old full in the process). I've seen many customers (and me also) use the rolling incrementals in the online recovery area to keep a full backup online from the previous day.
This is used with a second backup strategy for longer term storage to a backup device.
The way the RA handles this differently, is that it creates "virtual fulls" for each incremental backup you take. You also tell it how far back to store virtual fulls. Using this methodology, if you do an incremental backup nightly, you can keep "virtual fulls" from each night as far back as you want.
There is no need to keep an online backup, and one in backup appliance.
Why is the RA different from most backup strategies ?
1) The use of only needing to do incremental forevers uses less I/O to read database blocks, and less backup network I/O - Using this method, the RA ONLY needs the incremental backups to keep a restore point. This saves the I/O of doing a full, and it saves the bytes going across the network.
2) RMAN keeps track of all the backups. RMAN is the backbone of the RA, and the RA contains a recovery catalog. RMAN verifies that backups are good, and you will always know if you have a good backup to restore.
3) Real time apply. You can think of the RA receiving redo log information in the same vein as a Dataguard database. Without the RA, you would backup archive logs as they are written from the redo logs. This leaves you open to data loss from your backup.. The RA reads from the current Redo log stream in the database (like dataguard) to ensure there there is almost no data loss. Nothing else does this.
4) Performance. The performance the RA is phenomenal. You can find a whitepaper here on the performance with multiple databases backing up to a single RA appliance.
This is a fantastic product to backup multiple databases and most importantly be able to recover your databases with next-to-no data loss.
