ZDLRA Internals, Tables and Storage

ZDLRA tables are owned by rasys user and are one extension of rman recovery catalog views. The internal tables that were added are just a few, but are important to understand how tasks works (mainly INDEX_BACKUP). In this post, I will show tables like plans, plans_details, blocks, and chunks. And besides that, show a little glimpse about how the files are stored.

Extra tables

If you check, officially, the rman recovery catalog already includes some columns from ZDLRA, the column VB_KEY identify the virtual backup key inside ZDLRA. It exists in RC_BACKUP_PIECE as an example. The extra tables added are linked with SBT tasks (clone to tape or cloud), replication (to other ZDLRA), storage (chunks), vbdf and plans (virtual full backup).

The most import tables are listed below.

RASYS.VBDF: This table store the reference for virtual full backups created for the datafile. Have the information about the backup piece used as the source(base) for virtual full backup and the reference to the new backup piece that was generated at virtual full creation. The most import columns are:

  • VB_KEY: The unique identifier to virtual backup.
  • DF_KEY: The reference to datafile key for a virtual full backup.
  • CKP_ID and CKP_SCN: Checkpoint information (id/scn) for this virtual full backup.
  • SRCBP_KEY: The reference to the original backup piece (source) that was used to generate the virtual full backup. Links to table BP.
  • VCBP_KEY: Reference to the derived backup piece that was created during the index of the original (source) backup piece.

RASYS.PLANS: This table store the plans that link the datafile and the virtual full backup. Basically, is the reference “index” and links: virtual backup, datafile, and the number of chunks that store it. Important columns:

  • VB_KEY: The unique identifier to virtual backup.
  • DF_KEY: The reference to datafile key for virtual full backup.
  • NUMCHUNKS: Number of chunks used to store this virtual full backup.

RASYS.PLANS_DETAILS: IOT table that stores the detailed information for the plan for the “index”. It is partitioned over the DF_KEY column. Link the virtual full backup, datafile, block number, and chunk identification. Tells you in which chuck it is stored each block that are part of the virtual full backup. Import columns:

  • VB_KEY: The unique identifier to virtual backup.
  • DF_KEY: The reference to datafile key for virtual full backup.
  • BLOCKNO: Block number that is part of the datafile.
  • NUMBLKS: Number of the blocks (in sequential mode starting from BLOCKNO) that are equal/same.
  • CHUNKNO: What is the chunk id that store the BLOCKNO + NUMBKS.

RASYS.BLOCKS: IOT table that stores the info for each block that belongs to the datafile. It is partitioned over the DF_KEY column. There is no link to any backup, but store each version of a single block that is needed to restore any backup (the block number needed can be found in the PLAN_DETAILS and SCN come from other tables). Import columns:

  • DF_KEY: The reference to datafile key for virtual full backup.
  • BLOCKNO: Block number that is part of the datafile.
  • SCN and CKP_ID: Checkpoint and SCN for this specific version of the block.

RASYS.CHUNK: IOT table that has the information about the chunks that was used to store the backups for the datafile. Important columns:

  • DF_KEY: The reference to datafile key for virtual full backup.
  • CHUNKNO: What is the chunk id.
  • FILESIZE: Size for this chunk.
  • FILENAME: Derived file name that stores the chunk (no represent the file inside ASM).

These tables are the most important for ZDLRA for the internal part of ZDLRA. They are not needed in daily basis activities but I think that is useful if you want to understand how things work internally. The list above is just a glimpse for internal tables, but based on that you can easily: identify what are the datafile blocks that belongs for specific virtual backup, where the blocks are stored (which chunk), and how this virtual full backup was build (the plan that contains all the blocks).

Storage

As you saw above, the blocks are stored in chunks and in CHUNKS table we have filename information. But this is not related where the data are really stored, there are other places used too. All of these tables are stored at RA_POOL tablespace but don’t store the backup itself. The structure that does this is “CONTAINERS” and represent files inside ASM diskgroup.

If you see the ZDLRA doc (look the image below) this is called DELTA POOLS (CONTAINERS and CHUNKS) and is stored inside one “Delta Store” (ASM diskgroup). For ASM diskgroups you can see the CATALOG and DELTA. The CATALOG, as I wrote in this post, store the metadata information about the backups (mostly the rman catalog views) and the DELTA (the Delta Store) have the info related the backups itself.

For tablespaces, there are two important RA_POOL and RA_CATALOG. The tables listed before (in the “Extra Tables topic”) resides at RA_POOL tablespace. But the backup data itself is stored in CONTAINER files at DELTA diskgroup and you can check them in the table SYS.AMCONT$. Another option is going in ASM diskgroup and check the list at DELTA/CONTAINER files (each file have the default of 2TB):

ASMCMD> pwd
+DELTA/ZDLRA/CONTAINER
ASMCMD> ls -s
Block_Size      Blocks          Bytes          Space  Name
       512  4294959104  2199019061248  4398059094016  con.561.935405781
       512  4294959104  2199019061248  4398059094016  con.562.935405789
       512  4294959104  2199019061248  4398059094016  con.563.935405797
       512  4294959104  2199019061248  4398059094016  con.564.935405805
…
…
       512  4294959104  2199019061248  4398059094016  con.656.935406489
       512   308051968   157722607616   315692679168  con.657.935406495
ASMCMD>

You can see more info checking tables SYS.AM* tables and views (SYS.AMAU$, SYS.AMCONT$, and SYS.AM$CONTAINER are examples). The list for containers files are not even listed as ZDLRA database (as datafile in dba_data_files) but are created directly by ZDLRA library.

You can even test the performance (before starting to use ZDLRA usage) to create these files using rastat.pl: https://docs.oracle.com/cd/E88198_01/AMAGD/amagd_monitor.htm#AMAGD1503. And this is the only info in the docs about CONTAINERS files.

Last info about ZDLRA database and storage, the database operates in NOARCHIVLOG mode. The backups for it are daily exports from the metadata information and in case of corruption/lost you can reconstruct the information reading the con files.

Conclusion

Understand the tables involved for ZDLRA are important to see what’s happening internally, how the index is stored and how works virtual full backup. The tables listed above are not used in daily bases for ZDLRA, you usually go to rman catalog view (RC_*), everything is there.

But, PLANS, PLANS_DETAILS, and VCBP are the base for a task like INDEX_BACKUP and to sustain virtual full backups. I needed to pass over these tables before explaining in more details the virtual full creation and INDEX_BACKUP task.

The storage part, containers and ASM diskgroup are needed just to help support to identify some bottleneck or problem. You don’t need to use it but I think that it is important to show you, at least superficially, how its work.

 

Disclaimer: “The postings on this site are my own and don’t necessarily represent my actual employer positions, strategies or opinions. The information here was edited to be useful for general purpose, specific data and identifications were removed to allow reach the generic audience and to be useful for the community.”

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2 thoughts on “ZDLRA Internals, Tables and Storage

  1. Pingback: ZDLRA Internals, INDEX_BACKUP task in details | Blog Fernando Simon

  2. Pingback: ZDLRA Internals, Virtual Full Backup | Fernando Simon

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