NAME¶
memcached_mget - Retrieving data from the server
SYNOPSIS¶
#include <libmemcached/memcached.h>
- memcached_result_st *
memcached_fetch_result(memcached_st *ptr,
memcached_result_st *result,
memcached_return_t *error)
- char * memcached_get(memcached_st *ptr,
const char *key, size_t key_length,
size_t *value_length, uint32_t *flags,
memcached_return_t *error)
- memcached_return_t
memcached_mget(memcached_st *ptr, const char * const
*keys, const size_t *key_length,
size_t number_of_keys)
- char *
memcached_get_by_key(memcached_st *ptr, const char
*group_key, size_t group_key_length, const
char *key, size_t key_length,
size_t *value_length, uint32_t *flags,
memcached_return_t *error)
- memcached_return_t
memcached_mget_by_key(memcached_st *ptr, const char
*group_key, size_t group_key_length, const char *
const *keys, const size_t *key_length,
size_t number_of_keys)
- memcached_return_t
memcached_fetch_execute(memcached_st *ptr,
memcached_execute_fn *callback,
void *context, uint32_t
number_of_callbacks)
- memcached_return_t
memcached_mget_execute(memcached_st *ptr, const char *
const *keys, const size_t *key_length,
size_t number_of_keys,
memcached_execute_fn *callback, void
*context, uint32_t number_of_callbacks)
- memcached_return_t
memcached_mget_execute_by_key(memcached_st *ptr, const
char *group_key, size_t group_key_length, const
char * const *keys, const size_t *key_length,
size_t number_of_keys,
memcached_execute_fn *callback, void
*context, uint32_t number_of_callbacks)
- memcached_return_t (*memcached_execute_fn)(const
memcached_st *ptr, memcached_result_st *result,
void *context)
Compile and link with -lmemcached
DESCRIPTION¶
memcached_get() is used to fetch an individual value from the server. You
must pass in a key and its length to fetch the object. You must supply three
pointer variables which will give you the state of the returned object. A
uint32_t pointer to contain whatever flags you stored with the value, a
size_t pointer which will be filled with size of of the object, and a
memcached_return_t pointer to hold any error. The object will be
returned upon success and NULL will be returned on failure. Any object
returned by
memcached_get() must be released by the caller application.
memcached_mget() is used to select multiple keys at once. For multiple
key operations it is always faster to use this function. This function always
works asynchronously.
To retrieve data after a successful execution of
memcached_mget(), you
will need to call
memcached_fetch_result(). You should continue to call
this function until it returns a NULL (i.e. no more values). If you need to
quit in the middle of a
memcached_mget() call, you can execute a
memcached_quit(), those this is not required.
memcached_fetch_result() is used to fetch an individual value from the
server.
memcached_mget() must always be called before using this
method. You must pass in a key and its length to fetch the object. You must
supply three pointer variables which will give you the state of the returned
object. A
uint32_t pointer to contain whatever flags you stored with
the value, a
size_t pointer which will be filled with size of of the
object, and a
memcached_return_t pointer to hold any error. The object
will be returned upon success and NULL will be returned on failure.
MEMCACHED_END is returned by the *error value when all objects that
have been found are returned. The final value upon
MEMCACHED_END is
null.
memcached_fetch_result() is used to return a
memcached_result_st
structure from a memcached server. The result object is forward compatible
with changes to the server. For more information please refer to the
memcached_result_st help. This function will dynamically allocate a
result structure for you if you do not pass one to the function.
memcached_fetch_execute() is a callback function for result sets. Instead
of returning the results to you for processing, it passes each of the result
sets to the list of functions you provide. It passes to the function a
memcached_st that can be cloned for use in the called function (it can
not be used directly). It also passes a result set which does not need to be
freed. Finally it passes a "context". This is just a pointer to a
memory reference you supply the calling function. Currently only one value is
being passed to each function call. In the future there will be an option to
allow this to be an array.
memcached_mget_execute() and
memcached_mget_execute_by_key() is
similar to
memcached_mget(), but it may trigger the supplied callbacks
with result sets while sending out the queries. If you try to perform a really
large multiget with
memcached_mget() you may encounter a deadlock in
the OS kernel (it will fail to write data to the socket because the input
buffer is full).
memcached_mget_execute() solves this problem by
processing some of the results before continuing sending out requests. Please
note that this function is only available in the binary protocol.
memcached_get_by_key() and
memcached_mget_by_key() behave in a
similar nature as
memcached_get() and
memcached_mget(). The
difference is that they take a master key that is used for determining which
server an object was stored if key partitioning was used for storage.
All of the above functions are not tested when the
MEMCACHED_BEHAVIOR_USE_UDP has been set. Executing any of these
functions with this behavior on will result in
MEMCACHED_NOT_SUPPORTED
being returned, or for those functions which do not return a
memcached_return_t, the error function parameter will be set to
MEMCACHED_NOT_SUPPORTED.
RETURN¶
All objects retrieved via
memcached_get() or
memcached_get_by_key() must be freed with
free(3).
memcached_get() will return NULL on error. You must look at the value of
error to determine what the actual error was.
memcached_fetch_execute() return
MEMCACHED_SUCCESS if all keys
were successful.
MEMCACHED_NOTFOUND will be return if no keys at all
were found.
memcached_fetch_result() sets error to
MEMCACHED_END upon
successful conclusion.
MEMCACHED_NOTFOUND will be return if no keys at
all were found.
HOME¶
To find out more information please check:
http://libmemcached.org/
SEE ALSO¶
memcached(1) libmemcached(3) memcached_strerror(3)
AUTHOR¶
Brian Aker
COPYRIGHT¶
2011, Brian Aker DataDifferential,
http://datadifferential.com/