# Redis Function
This PR added the Redis Functions capabilities that were suggested on #8693.
The PR also introduce a big refactoring to the current Lua implementation
(i.e `scripting.c`). The main purpose of the refactoring is to have better
code sharing between the Lua implementation that exists today on Redis
(`scripting.c`) and the new Lua engine that is introduced on this PR.
The refactoring includes code movements and file name changes as well as some
logic changes that need to be carefully reviewed. To make the review easier,
the PR was split into multiple commits. Each commit is deeply described later on
but the main concept is that some commits are just moving code around without
making any logical changes, those commits are less likely to cause any issues
or regressions and can be reviewed fast. Other commits, which perform code and
logic changes, need to be reviewed carefully, but those commits were created
after the code movements so it's pretty easy to see what was changed. To sum up,
it is highly recommended to review this PR commit by commit as it will be easier
to see the changes, it is also recommended to read each commit description
(written below) to understand what was changed on the commit and whether or not
it's just a huge code movement or a logic changes.
## Terminology
Currently, the terminology in Redis is not clearly defined. Scripts refer to Lua
scripts and eval also refers only to Lua. Introducing Redis Function requires
redefining those terms to be able to clearly understand what is been discussed
on each context.
* eval - legacy Lua script implementation.
* Function - new scripting implementation (currently implemented in Lua but in
the future, it might be other languages like javascript).
* Engine - the component that is responsible for executing functions.
* Script - Function or legacy Lua (executed with `eval` or `evalsha`)
## Refactoring New Structure
Today, the entire scripting logic is located on `scripting.c`. This logic can
be split into 3 main groups:
1. Script management - responsible for storing the scripts that were sent to
Redis and retrieving them when they need to be run (base on the script sha
on the current implementation).
2. Script invocation - invoke the script given on `eval` or `evalsha` command
(this part includes finding the relevant script, preparing the arguments, ..)
3. Interact back with Redis (command invocation)
Those 3 groups are tightly coupled on `scripting.c`. Redis Functions also need
to use those groups logics, for example, to interact back with Redis or to
execute Lua code. The refactoring attempts to split those 3 groups and define
APIs so that we can reuse the code both on legacy Lua scripts and Redis Functions.
In order to do so we define the following units:
1. script.c: responsible for interaction with Redis from within a script.
2. script_lua.c: responsible to execute Lua code, uses `script.c` to interact
with Redis from within the Lua code.
3. function_lua.c: contains the Lua engine implementation, uses `script_lua.c`
to execute the Lua code.
4. functions.c: Contains Redis Functions implementation (`FUNCTION` command,),
uses `functions_lua.c` if the function it wants to invoke needs the Lua
engine.
4. eval.c: the original `scripting.c` contains the Lua legacy implementation and
was refactored to use `script_lua.c` to invoke the Lua code.
## Commits breakdown
Notice: Some small commits are omitted from this list as they are small and
insignificant (for example build fixes)
### First commit - code movements
This commit rename `scripting.c` -> `eval.c` and introduce the new `script_lua.c`
unit. The commit moves relevant code from `eval.c` (`scripting.c`) to
`script_lua.c`, the purpose of moving the code is so that later we will be able
to re-use the code on the Lua engine (`function_lua.c`). The commit only moves
the code without modifying even a single line, so there is a very low risk of
breaking anything and it also makes it much easier to see the changes on the
following commits.
Because the commit does not change the code (only moves it), it does not compile.
But we do not care about it as the only purpose here is to make the review
processes simpler.
### Second commit - move legacy Lua variables into `eval.c`
Today, all Lua-related variables are located on the server struct. The commit
attempt to identify those variable and take them out from the server struct,
leaving only script related variables (variables that later need to be used
also by engines)
The following variable where renamed and left on the server struct:
* lua_caller -> script_caller
* lua_time_limit -> script_time_limit
* lua_timedout -> script_timedout
* lua_oom -> script_oom
* lua_disable_deny_script -> script_disable_deny_script
* in_eval -> in_script
The following variables where moved to lctx under eval.c
* lua
* lua_client
* lua_cur_script
* lua_scripts
* lua_scripts_mem
* lua_replicate_commands
* lua_write_dirty
* lua_random_dirty
* lua_multi_emitted
* lua_repl
* lua_kill
* lua_time_start
* lua_time_snapshot
This commit is in a low risk of introducing any issues and it is just moving
variables around and not changing any logic.
### Third commit - introducing script unit
This commit introduces the `script.c` unit. Its purpose (as described above) is
to provide an API for scripts to interact with Redis. Interaction includes
mostly executing commands, but also other functionalities. The interaction is
done using a `ScriptRunCtx` object that needs to be created by the user and
initialized using `scriptPrepareForRun`. A detailed list of functionalities
expose by the unit:
1. Calling commands (including all the validation checks such as
acl, cluster, read only run, ...)
2. Set Resp
3. Set Replication method (AOF/REPLICATION/NONE)
4. Call Redis back on long-running scripts to allow Redis to reply to clients
and perform script kill
The commit introduces the new unit and uses it on eval commands to interact with
Redis.
### Fourth commit - Moved functionality of invoke Lua code to `script_lua.c`
This commit moves the logic of invoking the Lua code into `script_lua.c` so
later it can be used also by Lua engine (`function_lua.c`). The code is located
on `callFunction` function and assumes the Lua function already located on the
top of the Lua stack. This commit also change `eval.c` to use the new
functionality to invoke Lua code.
### Fith commit - Added Redis Functions unit (`functions.c`) and Lua engine
(`function_lua.c`)
Added Redis Functions unit under `functions.c`, included:
1. FUNCTION command:
* FUNCTION CREATE
* FUNCTION CALL
* FUNCTION DELETE
* FUNCTION KILL
* FUNCTION INFO
* FUNCTION STATS
2. Register engines
In addition, this commit introduces the first engine that uses the Redis
Functions capabilities, the Lua engine (`function_lua.c`)
## API Changes
### `lua-time-limit`
configuration was renamed to `script-time-limit` (keep `lua-time-limit` as alias
for backward compatibility).
### Error log changes
When integrating with Redis from within a Lua script, the `Lua` term was removed
from all the error messages and instead we write only `script`. For example:
`Wrong number of args calling Redis command From Lua script` -> `Wrong number
of args calling Redis command From script`
### `info memory` changes:
Before stating all the changes made to memory stats we will try to explain the
reason behind them and what we want to see on those metrics:
* memory metrics should show both totals (for all scripting frameworks), as well
as a breakdown per framework / vm.
* The totals metrics should have "human" metrics while the breakdown shouldn't.
* We did try to maintain backward compatibility in some way, that said we did
make some repurpose to existing metrics where it looks reasonable.
* We separate between memory used by the script framework (part of redis's
used_memory), and memory used by the VM (not part of redis's used_memory)
A full breakdown of `info memory` changes:
* `used_memory_lua` and `used_memory_lua_human` was deprecated,
`used_memory_vm_eval` has the same meaning as `used_memory_lua`
* `used_memory_scripts` was renamed to `used_memory_scripts_eval`
* `used_memory_scripts` and `used_memory_scripts_human` were repurposed and now
return the total memory used by functions and eval (not including vm memory,
only code cache, and structs).
* `used_memory_vm_function` was added and represents the total memory used by
functions vm's
* `used_memory_functions` was added and represents the total memory by functions
(not including vm memory, only code cache, and structs)
* `used_memory_vm_total` and `used_memory_vm_total_human` was added and
represents the total memory used by vm's (functions and eval combined)
### `functions.caches`
`functions.caches` field was added to `memory stats`, representing the memory
used by engines that are not functions (this memory includes data structures
like dictionaries, arrays, ...)
## New API
### FUNCTION CREATE
Usage: FUNCTION CREATE `ENGINE` `NAME` `[REPLACE]` `[DESC <DESCRIPTION>]` `<CODE>`
* `ENGINE` - The name of the engine to use to create the script.
* `NAME` - the name of the function that can be used later to call the function
using `FUNCTION CALL` command.
* `REPLACE` - if given, replace the given function with the existing function
(if exists).
* `DESCRIPTION` - optional argument describing the function and what it does
* `CODE` - function code.
The command will return `OK` if created successfully or error in the following
cases:
* The given engine name does not exist
* The function name is already taken and `REPLACE` was not used.
* The given function failed on the compilation.
### FCALL and FCALL_RO
Usage: FCALL/FCALL_RO `NAME` `NUM_KEYS key1 key2` … ` arg1 arg2`
Call and execute the function specified by `NAME`. The function will receive
all arguments given after `NUM_KEYS`. The return value from the function will
be returned to the user as a result.
* `NAME` - Name of the function to run.
* The rest is as today with EVALSHA command.
The command will return an error in the following cases:
* `NAME` does not exist
* The function itself returned an error.
The `FCALL_RO` is equivalent to `EVAL_RO` and allows only read-only commands to
be invoked from the script.
### FUNCTION DELETE
Usage: FUNCTION DELETE `NAME`
Delete a function identified by `NAME`. Return `OK` on success or error on one
of the following:
* The given function does not exist
### FUNCTION INFO
Usage: FUNCTION INFO `NAME` [WITHCODE]
Return information about a function by function name:
* Function name
* Engine name
* Description
* Raw code (only if WITHCODE argument is given)
### FUNCTION LIST
Usage: FUNCTION LIST
Return general information about all the functions:
* Function name
* Engine name
* Description
### FUNCTION STATS
Usage: FUNCTION STATS
Return information about the current running function:
* Function name
* Command that was used to invoke the function
* Duration in MS that the function is already running
If no function is currently running, this section is just a RESP nil.
Additionally, return a list of all the available engines.
### FUNCTION KILL
Usage: `FUNCTION KILL`
Kill the currently executing function. The command will fail if the function
already initiated a write command.
## Notes
Note: Function creation/deletion is replicated to AOF but AOFRW is not
implemented sense its going to be removed: #9794
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