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I am a bit confused with the term, a byte offset value, which is treated as map key in Hadoop Map reduce program.
First, what is the byte offset value?
Second, how is it generated, and how does one view this byte-offset value?
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In computer science, offset describes the location of a piece of data compared to another location. For example, when a program is accessing an array of bytes, the fifth byte is offset by four bytes from the array's beginning.
the byte address / number of bytes per block. The cache block number = the memory block number modulo the number of blocks in the cache. The block offset (i.e., word offset) = the word address modulo the number of words per block.
Is Offset In Bits Or Bytes? There are two answers to this question. Whence adds offset to the position specified by whence, fseek takes offset as the number of bytes, not bits: The new position, measured in bytes from the beginning of the file, will be obtained by adding offset to the position specified by whence.
The byte offset is just the count of the bytes, starting at 0. The big question is: how are the 16-bit offsets for the branch instructions calculated. The big answer is: count the number of bytes to the destination. The first branch is in instruction 7 in the IJVM code, and at offset 11 in the hex byte code.
byte offset is the number of character that exists counting from the beginning of a line.
for example, this line
what is byte offset?
will have a byte offset of 19. This is used as key value in hadoop
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Basically an offset is an integer which is used to find the distance ( absolute address) with respect to the base address.
Assume a Text file with the following data
Computer-science World
Quantum Computing
now the offset for the first line is 0 and the input to the hadoop job will be <0,Computer Science World> for the second line the offset will be <23,Quantum Computing>
whenever we pass the text file to hadoop job. It internally calculates the byte offset.
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The byte offset is the count of bytes starting at zero. One character or space is usually one byte when talking about Hadoop. But check out this question if you want to know more: How many bits in a character?
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