Me by ushing dirty metadata back to disk in the

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Unformatted text preview: 13 Large Directory Support (6/6) Extensible hashing CS480 Principles of Data Management h(n) = n as a binary number •  As a directory grows 2 –  Extensible hashing adds new directory blocks one at a .me •  Create opera.ons finds no more room in the directory block designated by the hash value of the new name –  Splits the block into two –  Finding the logical block number (bucket) of the new directory block (bucket): •  Add ‘1’ in the n+1st bit from the least significant bit (n is the local depth) •  Directory entries with a ‘1’ in the n+1st bit from the least significant bit of their hash value are moved to the new block •  No change for other entries •  Lookup requires only a single directory block access –  O(1) CS480 Principles of Data Management 000 Spring 2013 001 010 011 100 101 110 111 2 64 44 Bucket A 2 9 25 Bucket B 5 2 10 Bucket C 3 3 Bucket D 3 31 15 7 63 Bucket D’ Local depth Bucket A 64 44 Global depth 2 2 9 00 25 5 Bucket B 2 01 Bucket C 10 10 2 11 3 Insert 63 Large Directory Support (2/6) Extensible hashing 3 Spring 2013 Large Directory Support (2/6) Extensible hashing 31 15 7 Bucket D Global depth: 2 Local depth for Bucket A~ D :2 CS480 Principles of Data Management Spring 2013 Logging and Recovery •  Journaling –  GPFS records all metadata updates that affect file system consistency in a journal or write ­ahead log •  Each node has a separate log for each file system it mounts •  This log can be read by all other nodes •  Any node can perform recovery on behalf of a failed node –  Not necessary to wait for the failed node to recover •  Logs can be fixed size –  Space in the log can be freed up at any .me by flushing dirty metadata back to disk in the background 4 2/1/13 CS480 Pr...
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