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improved availabilitythe data in a distributed system may be replicated so that it is at more than one site thus the failure of a node or a
improved reliabilityin a centralised dbms a server failure stops the operations of the dbms though a failure at single site of a ddbms or a failure
as we have discussed page tables map virtual page addresses to physical page addresses one of the advantages of using virtual addresses is that we
reflects organisational structuremany organizations are distributed over various locations if an organisation has many offices in dissimilar cities
suppose your process starts up and allocates some memory with malloc the allocator will then give part of a memory page to your process the os then
distributed control and data sharingthe geographical distribution of an organization can be showed in the distribution of the data if a number of
when do we write a page from physical memory back to the diskin general caches have two broad types of writing policies one approach is a
advantages of data distributionthe primary benefit of distributed database systems is the ability to access and share data in a reliable and
advantages and drawbacks of ddbms there are various reasons for building distributed database systems with sharing of data reliability and
a distributed transactionlet us demonstrate the concept of a distributed transaction by considering a banking system having of three branches located
for reading most operating systems use demand paging this means that pages are only read from the disk into physical memory when they are needed in
we will briey introduce paging to nish off this lecture when a process is loaded not all of the pages are immediately loaded since its possible that
need for distributed database systemsa distributed database is a set of database kept on multiple computers that appears to applications as a one
objectives differentiate ddbms and conventional dbms describe network topology for ddbms describe the concepts of horizontal and vertical
distributed and client server databasesintroductionthis unit tells the distributed database systems which are primarily relational and one important
how exactly is a page table used to look up an addressthe cpu has a page table base register ptbrwhich points to the base entry 0 of the level-0 page
multi-level page tables are tree-like structures to hold page tables as an example consider a two- level page table again on a 32-bit architecture
as mentioned above page tables are lookup tables mapping a process virtual pages to physical pages in ram how would one implement these page
virtual addresses are made up of two parts the rst part is the page number and the second part is an offset inside that page suppose our pages are
when a program issues a memory load or store operation the virtual addresses vas used in those operations have to be translated into real physical
using pages makes it easier to manage the whole memory avoiding excessive fragmentation and waste as an analogy think of tetris but with only square
applications allocate memory in terms of the number of bytes that they need but this level of granularity is too ne-grained for the operating system
in modern operating systems applications do not directly access the physical memory instead they use so-called virtual memory where each virtual
while it is hard to resolve a deadlock which has been detected fortunately it is fairly easy to prevent deadlocks from ever happening the key is that
deadlocks can be detected while the program is running by running cycle detection algorithms on the graph that denes the current use of resourcesdene