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ngx_http_lua_share_dict

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Installation
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Nginx shared dict API for Lua
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- English Mailing List
- Chinese Mailing List
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Notice

Please notice that only applies to their own block in init_by_lua phase, because some shdict maybe not init yet.

Installation

Directives

lua_shared_mem

lua_shared_mem

syntax: lua_shared_mem <name> <size>

default: no

context: http

phase: depends on usage

Declares a shared memory zone, <name>, to serve as storage for the shm.

Shared memory zones are always shared by all the nginx worker processes in the current nginx server instance.

The <size> argument accepts size units such as k and m:


 http {
     lua_shared_mem dict 10m;
     ...
 }

Use following script to get the Lua table:

  local t = require('resty.shdict')
  local dict = t.dict

Following example will be based on the above settings.

See Nginx shared dict API for Lua for details.

The hard-coded minimum size is 8KB while the practical minimum size depends on actual user data set (some people start with 12KB).

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Nginx shared dict API for Lua

The resulting object dict has the following methods:

get
get_stale
set
safe_set
add
safe_add
replace
delete
incr
lpush
rpush
lpop
rpop
llen
flush_all
flush_expired
get_keys
expire
ttl

get

syntax: value, flags = dict:get(key)

context: init_by_lua*, init_worker_by_lua*, set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua*, body_filter_by_lua*, log_by_lua*, ngx.timer.*, balancer_by_lua*, ssl_certificate_by_lua*, ssl_session_fetch_by_lua*, ssl_session_store_by_lua*

Retrieving the value in the dictionary dict for the key key. If the key does not exist or has expired, then nil will be returned.

In case of errors, nil and a string describing the error will be returned.

The value returned will have the original data type when they were inserted into the dictionary, for example, Lua booleans, numbers, or strings.

The first argument to this method must be the dictionary object itself, for example,


 local value, flags = dict.get(dict, "Marry")

or use Lua's syntactic sugar for method calls:


 local value, flags = dict:get("Marry")

These two forms are fundamentally equivalent.

If the user flags is 0 (the default), then no flags value will be returned.

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get_stale

syntax: value, flags, stale = dict:get_stale(key)

context: set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua*, body_filter_by_lua*, log_by_lua*, ngx.timer.*, balancer_by_lua*, ssl_certificate_by_lua*, ssl_session_fetch_by_lua*, ssl_session_store_by_lua*

Similar to the get method but returns the value even if the key has already expired.

Returns a 3rd value, stale, indicating whether the key has expired or not.

Note that the value of an expired key is not guaranteed to be available so one should never rely on the availability of expired items.

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set

syntax: success, err, forcible = dict:set(key, value, exptime?, flags?)

context: init_by_lua*, set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua*, body_filter_by_lua*, log_by_lua*, ngx.timer.*, balancer_by_lua*, ssl_certificate_by_lua*, ssl_session_fetch_by_lua*, ssl_session_store_by_lua*

Unconditionally sets a key-value pair into the shm-based dictionary dict. Returns three values:

success: boolean value to indicate whether the key-value pair is stored or not.
err: textual error message, can be "no memory".
forcible: a boolean value to indicate whether other valid items have been removed forcibly when out of storage in the shared memory zone.

The value argument inserted can be Lua booleans, numbers, strings, or nil. Their value type will also be stored into the dictionary and the same data type can be retrieved later via the get method.

The optional exptime argument specifies expiration time (in seconds) for the inserted key-value pair. The time resolution is 0.001 seconds. If the exptime takes the value 0 (which is the default), then the item will never expire.

The optional flags argument specifies a user flags value associated with the entry to be stored. It can also be retrieved later with the value. The user flags is stored as an unsigned 32-bit integer internally. Defaults to 0. The user flags argument was first introduced in the v0.5.0rc2 release.

When it fails to allocate memory for the current key-value item, then set will try removing existing items in the storage according to the Least-Recently Used (LRU) algorithm. Note that, LRU takes priority over expiration time here. If up to tens of existing items have been removed and the storage left is still insufficient (either due to the total capacity limit specified by lua_shared_dict or memory segmentation), then the err return value will be no memory and success will be false.

If this method succeeds in storing the current item by forcibly removing other not-yet-expired items in the dictionary via LRU, the forcible return value will be true. If it stores the item without forcibly removing other valid items, then the return value forcible will be false.

The first argument to this method must be the dictionary object itself, for example,


 local succ, err, forcible = dict.set(dict, "Marry", "it is a nice cat!")

or use Lua's syntactic sugar for method calls:


 local succ, err, forcible = dict:set("Marry", "it is a nice cat!")

These two forms are fundamentally equivalent.

Please note that while internally the key-value pair is set atomically, the atomicity does not go across the method call boundary.

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safe_set

syntax: ok, err = dict:safe_set(key, value, exptime?, flags?)

Similar to the set method, but never overrides the (least recently used) unexpired items in the store when running out of storage in the shared memory zone. In this case, it will immediately return nil and the string "no memory".

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add

syntax: success, err, forcible = dict:add(key, value, exptime?, flags?)

Just like the set method, but only stores the key-value pair into the dictionary dict if the key does not exist.

If the key argument already exists in the dictionary (and not expired for sure), the success return value will be false and the err return value will be "exists".

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safe_add

syntax: ok, err = dict:safe_add(key, value, exptime?, flags?)

Similar to the add method, but never overrides the (least recently used) unexpired items in the store when running out of storage in the shared memory zone. In this case, it will immediately return nil and the string "no memory".

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replace

syntax: success, err, forcible = dict:replace(key, value, exptime?, flags?)

Just like the set method, but only stores the key-value pair into the dictionary dict if the key does exist.

If the key argument does not exist in the dictionary (or expired already), the success return value will be false and the err return value will be "not found".

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delete

syntax: dict:delete(key)

Unconditionally removes the key-value pair from the shm-based dictionary dict.

It is equivalent to dict:set(key, nil).

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incr

syntax: newval, err, forcible? = dict:incr(key, value, init?, exptime?)

Increments the (numerical) value for key in the shm-based dictionary dict by the step value value. Returns the new resulting number if the operation is successfully completed or nil and an error message otherwise.

When the key does not exist or has already expired in the shared dictionary,

if the init argument is not specified or takes the value nil, this method will return nil and the error string "not found", or
if the init argument takes a number value, this method will create a new key with the value init + value.

The optional exptime argument specifies expiration time for key,

if the exptime takes a number greater than 0, then the item will set expire by this number, or
if the exptime takes a number less than 0, then the item will be set to never expire, or
if the exptime takes the value 0 (which is the default), then the item's ttl will not change.

Like the add method, it also overrides the (least recently used) unexpired items in the store when running out of storage in the shared memory zone.

The forcible return value will always be nil when the init argument is not specified.

If the original value is not a valid Lua number in the dictionary, it will return nil and "not a number".

The value argument and init argument can be any valid Lua numbers, like negative numbers or floating-point numbers.

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lpush

syntax: length, err = dict:lpush(key, value)

Inserts the specified (numerical or string) value at the head of the list named key in the shm-based dictionary dict. Returns the number of elements in the list after the push operation.

If key does not exist, it is created as an empty list before performing the push operation. When the key already takes a value that is not a list, it will return nil and "value not a list".

It never overrides the (least recently used) unexpired items in the store when running out of storage in the shared memory zone. In this case, it will immediately return nil and the string "no memory".

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rpush

syntax: length, err = dict:rpush(key, value)

Similar to the lpush method, but inserts the specified (numerical or string) value at the tail of the list named key.

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lpop

syntax: val, err = dict:lpop(key)

Removes and returns the first element of the list named key in the shm-based dictionary dict.

If key does not exist, it will return nil. When the key already takes a value that is not a list, it will return nil and "value not a list".

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rpop

syntax: val, err = dict:rpop(key)

Removes and returns the last element of the list named key in the shm-based dictionary dict.

If key does not exist, it will return nil. When the key already takes a value that is not a list, it will return nil and "value not a list".

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llen

syntax: len, err = dict:llen(key)

Returns the number of elements in the list named key in the shm-based dictionary dict.

If key does not exist, it is interpreted as an empty list and 0 is returned. When the key already takes a value that is not a list, it will return nil and "value not a list".

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flush_all

syntax: dict:flush_all()

Flushes out all the items in the dictionary. This method does not actuall free up all the memory blocks in the dictionary but just marks all the existing items as expired.

flush_expired

syntax: flushed = dict:flush_expired(max_count?)

Flushes out the expired items in the dictionary, up to the maximal number specified by the optional max_count argument. When the max_count argument is given 0 or not given at all, then it means unlimited. Returns the number of items that have actually been flushed.

Unlike the flush_all method, this method actually free up the memory used by the expired items.

get_keys

syntax: keys = dict:get_keys(max_count?)

Fetch a list of the keys from the dictionary, up to <max_count>.

By default, only the first 1024 keys (if any) are returned. When the <max_count> argument is given the value 0, then all the keys will be returned even there is more than 1024 keys in the dictionary.

WARNING Be careful when calling this method on dictionaries with a really huge number of keys. This method may lock the dictionary for quite a while and block all the nginx worker processes that are trying to access the dictionary.

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expire

syntax: ret, stale = dict:expire(key, exptime, force?)

Set a key's time to live in seconds. The time resolution is 0.001 seconds. If the exptime takes the value 0 , then the item will never expire.

The optional force argument is given true can set stale key' time to live forcedly, reference (get_stale)[#get_stale].

1 means expire key successfully, if key does not exist or key is expired, it will return 0.

If ret equal to 1, the 2nd returns, stale, indicating whether the key has expired or not.

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ttl

syntax: keys = dict:ttl(key)

Get the time to live for key.

If key does not exist, it will return -1, and if key is expired, it will return -2.

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Community

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English Mailing List

The openresty-en mailing list is for English speakers.

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Chinese Mailing List

The openresty mailing list is for Chinese speakers.

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Bugs and Patches

Please report bugs or submit patches by

creating a ticket on the GitHub Issue Tracker,
or posting to the OpenResty community.

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Author

Jinhua Tan.

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Copyright and License

This module is licensed under the BSD license.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

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Awesome

Name

Table of Contents

Notice

Installation

Directives

lua_shared_mem

Nginx shared dict API for Lua

get

get_stale

set

safe_set

add

safe_add

replace

delete

incr

lpush

rpush

lpop

rpop

llen

flush_all

flush_expired

get_keys

expire

ttl

Community

English Mailing List

Chinese Mailing List

Bugs and Patches

Author

Copyright and License

See Also