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Kenneth Reitz
70 lines
2.5 KiB
ReStructuredText
70 lines
2.5 KiB
ReStructuredText
`|Redis Documentation| <index.html>`_
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**SetrangeCommand: Contents**
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`SETRANGE \_key\_ \_offset\_ \_value\_ (Redis > <#SETRANGE%20_key_%20_offset_%20_value_%20(Redis%20%3E>`_
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`Examples <#Examples>`_
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`Patterns <#Patterns>`_
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`Return value <#Return%20value>`_
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SetrangeCommand
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===============
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#sidebar `StringCommandsSidebar <StringCommandsSidebar.html>`_
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SETRANGE \_key\_ \_offset\_ \_value\_ (Redis >
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==============================================
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2.1.8) =
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*Time complexity: O(1) not counting the time taken to copy the new string in place, as usually this string is small so the amoritzed time is O(1). Otheriwse O(M) with M being the length of the value argument*
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Overwrites part of a string at *key* starting at the specified
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offset,for all the length of *value*.If the offset is over the old
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length of the string, the string is paddedwith zero bytes until
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needed. Non existing keys are considered likealready containing an
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empty string.
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Examples
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--------
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First example, basic usage setting a range.
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::
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redis> set foo "Hello World"
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OK
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redis> setrange foo 6 "Redis"
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(integer) 11
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redis> get foo
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"Hello Redis"
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Example of the zero padding behavior.
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::
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redis> del foo
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(integer) 1
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redis> setrange foo 10 bar
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(integer) 13
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redis> get foo
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"\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00bar"
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Note that the maximum offset that you can set is 536870911 as Redis
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Strings are limited to 512 megabytes. You can still create longer
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arrays of values using multiple keys.
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**Warning**: When setting the last possible byte and the string
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value stored at *key* does not yet hold a string value, or holds a
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small string value, Redis needs to allocate all intermediate memory
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which can block the server for some time. On a 2010 Macbook Pro,
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setting byte number 536870911 (512MB allocation) takes ~300ms,
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setting byte number 134217728 (128MB allocation) takes ~80ms,
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setting bit number 33554432 (32MB allocation) takes ~30ms and
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setting bit number 8388608 (8MB allocation) takes ~8ms. Note that
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once this first allocation is done, subsequent calls to SETRANGE
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for the same *key* will not have the allocation overhead.
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Patterns
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--------
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Thanks to SETRANGE and the analogous GETRANGE command you can use
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Redis strings as a linear array of memory with O(1) random access.
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This is a very fast and efficient storage in many real world use
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cases.
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Return value
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------------
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`Integer reply <ReplyTypes.html>`_, specifically: the length of the
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string after it was modified by the command.
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.. |Redis Documentation| image:: redis.png |