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  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 2

Motivations  Tendency points to even bigger increase 3

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 4

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) 5

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) 6

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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 8

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 9 LFN GUID PFN

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) 10

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 11

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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) 13

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 (AliEn test set)  ALICE_TEST prepared in July to ‘really’ test 14

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 15

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 16