To what extent does Sun NFS deviate from one-copy file update semantics? Construct a scenario
in which two user-level processes sharing a file would operate correctly in a single UNIX host but
would observe inconsistencies when running in different hosts.
What will be an ideal response?
After a write operation, the corresponding data cached in clients other than the one performing the write is
invalid (since it does not reflect the current contents of the file on the NFS server), but the other clients will
not discover the discrepancy and may use the stale data for a period of up to 3 seconds (the time for which
cached blocks are assumed to be fresh). For directories, the corresponding period is 30 seconds, but the
consequences are less serious because the only operations on directories are to insert and delete file names.
Scenario: any programs that depend on the use of file data for synchronization would have problems. For
example, program A checks and sets two locks in a set of lock bits stored at the beginning of a file, protecting
records within the file. Then program A updates the two locked records. One second later program B reads the
same locks from its cache, finds them unset, sets them and updates the same records. The resulting values of
the two records are undefined.
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In the address bar, the ________ which is the sequence of folders that lead to the current file or folder location is indicated.
a. path b. address c. file d. description
Irene is working on a database that stores customer data and order information. The Customer Information Table holds customer information. A unique customer number serves as the primary key for this table. The Order Information Table holds order information. A unique order number serves as the primary key for this table. A customer only has one customer number but may have several order numbers
If Irene wants to establish a one-to-many relationship between the customer information table and the order information table, which of the following steps should she follow? A) Irene should include the foreign key in the customer information table as a primary key in the order information table. B) Irene should include the primary key in the customer information table as a foreign key in the order information table. C) Irene cannot establish a relationship between the two tables. D) Irene should include the primary key in the customer information table as a primary key in the order information table.