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Creating a simplified global unique file catalogue

Creating a simplified global unique file catalogue . Miguel Martinez Pedreira Pablo Saiz. Motivations. Reaching memory limits in the actual catalogue database machine(s) Catalogue is now ~700 Gigabytes Some tables are too large (in G#L and L#L) e.g. G132L – 55 GB, tried to split

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Creating a simplified global unique file catalogue

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  1. Creating a simplified global unique file catalogue Miguel Martinez Pedreira Pablo Saiz

  2. Motivations • Reaching memory limits in the actual catalogue database machine(s) • Catalogue is now ~700 Gigabytes • Some tables are too large (in G#L and L#L) • e.g. G132L – 55 GB, tried to split • Conversion old-catalogue to new-catalogue takes too long • Between 15 and 20 hours • Stuck on some of these large tables • Several mysql configurations (threads, memory, pools...) • Tried on alientest03 and alientest07 • Helped to find things that shouldn’t be there • In search of better performance

  3. Motivations • Tendency points to even bigger increase

  4. Previous status • Catalogue implementing several-host database • In order to separate the database into different machines • Never used in practice: users and data in the same host • Hosts Index • No referential integrity

  5. Current status (production) • Only references between G#L_REF and G#L_PFN with G#L, and them with SE • Found some entries that shouldn’t be there • e.g. PFNs with GUIDs that don’t exist • some unused or temporary tables (old functionalities, L#L without _s) • ~250L tables (x3) • ~100 G tables (x4)

  6. Improvements • Complete referential integrity: FKs all around • consistent database • InnoDB tables • row level locking • using ids (instead of text fields) for referencing • normalized data, surrogated keys • Cleaning tables, renaming fields • Fixing some keys • Lead to v2-20 version (currently in PANDA)

  7. x 100 x 250 Link to documentation!

  8. How to improve • New (Pablo’s) idea: Filesystem catalogue • No database, instead the catalogue is a UNIX-like filesystem • Using metadata files to keep the necessary information • aggregating this information was quite similar to having the DB itself... • Tried/discussed about different available filesystems • dealing with inodes, file limits, performance... • Performance was measured • unfortunately, it was too slow • What else? -> guidless catalogue

  9. GUIDs • GUID = Global Unique IDentifier • First decided to have GUIDs, because it was expected that LFNs would change the name very often, and GUIDs were something static • They give flexibility and functionalities • Very nice for mirroring • Permissions per LFN and per GUID • e.g. for having reduced permissions on links • Being used for the quotas too • BUT: not really used in practice, and adds quite a lot of complexity compared to the benefits PFN LFN GUID PFN LFN PFN

  10. Deleting GUIDs • We plan to use the LFN combined with the timestamp to maintain its uniqueness • So you can differ between them when they are deleted and a new LFN with the same name is registered • File naming for storage in SEs was based on GUIDs • now is LFN+timestamp: more human-readable • Simplicity • 240GB directly gone (~35% DB)

  11. Links • At this moment we have the ‘special’ PFN ‘guid://’ for handling links • A link is a LFN pointing to other LFN • Using GUIDs is more flexible (- consistent) • Our design implies pointing inside the same index: but is the use case in production (job outputs and archives). • This change helps us to get rid of 65% of the PFN entries-> 65% of 160GB = 100GB • Slightly different from UNIX symlinks, AliEn links point to part of an archive, not the full file

  12. x 100 x 250 Link to documentation! linkId

  13. Expectations • GUIDs gone, LFNs stay the same, PFN significantly reduced • if there was consistency, GUIDs should be below LFNs • 35% PFNs (350000) should be similar to the number of stored files in SEs (310000)

  14. Expectations • We get rid of ~50% of the catalogue in terms of size (240GB from GUIDs + 100GB from links) • Performance based on all the changes expected to really increase • We’ve had good experience with the TaskQueue • Looks like simple changes from a high-level view • but it involves a lot of effort to check and adapt the code • GUIDs everywhere  • Found old, miss working, improvable code • When? • May-Jun all tests working (AliEntest set) • ALICE_TEST prepared in July to ‘really’ test

  15. Testing • Desired a production-like environment • Not only for the new catalogue, but any change in AliEn • Going back to ALICE_TEST • Already had first stages of trains and standard jobs running • We want to synchronize the test catalogue with the production one • And to execute production jobs • We know is not that easy and beautiful (e.g. API) • Aiming to have newer versions of AliEn in production • In a ‘safe’ way • Test cases are very hard to cover

  16. To sum up • File Catalogue is getting unmaintainable • Is a critical part in AliEn • Some improvements implemented, we need more • Moving to a GUIDless catalogue • Planning to have production-like testing • and newer versions easier

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