mirror of https://github.com/redis/redis.git
aed879ad0a
# Description
Add optimistic locking for string objects via compare-and-set and
compare-and-delete mechanism.
## What's changed
Introduction of new DIGEST command for string objects calculated via
XXH3 hash.
Extend SET command with new parameters supporting optimistic locking.
The new value is set only if checks against a given (old) value or a
given string digest pass.
Introduction of new DELEX command to support conditionally deleting a
key. Conditions are also checks against string value or string digest.
## Motivation
For developers who need to to implement a compare-and-set and
compare-and-delete single-key optimistic concurrency control this PR
provides single-command based implementation.
Compare-and-set and compare-and-delete are mostly used for [Optimistic
concurrency
control](https://en.wikipedia.org/wiki/Optimistic_concurrency_control):
a client (1) fetches the value, keeps the old value (or its digest, for
a large string) in memory, (2) manipulates a local copy of the value,
(3) applies the local changes to the server, but only if the server’s
value hasn’t been changed (still equal to the old value).
Note that compare-and-set [can also be
implemented](https://redis.io/docs/latest/develop/using-commands/transactions/#optimistic-locking-using-check-and-set)
with WATCH … MULTI … EXEC and Lua scripts. The new SET optional
arguments and the DELEX command do not enable new functionality,
however, they are much simpler and faster to use for the very common use
case of single-key optimistic concurrency control.
## Related issues and PRs
https://github.com/redis/redis/issues/12485
https://github.com/redis/redis/pull/8361
https://github.com/redis/redis/pull/4258
## Description of the new commands
### DIGEST
```
DIGEST key
```
Get the hash digest of the value stored in key, as an hex string.
Reply:
- Null if key does not exist
- error if key exists but holds a value which is not a string
- (bulk string) the XXH3 digest of the value stored in key, as an hex
string
### SET
```
SET key value [NX | XX | IFEQ match-value | IFNE match-value | IFDEQ match-digest | IFDNE match-digest] [GET] [EX seconds | PX milliseconds | EXAT unix-time-seconds | PXAT unix-time-milliseconds | KEEPTTL]
```
`IFEQ match-value` - Set the key’s value and expiration only if its
current value is equal to match-value. If key doesn’t exist - it won’t
be created.
`IFNE match-value` - Set the key’s value and expiration only if its
current value is not equal to match-value. If key doesn’t exist - it
will be created.
`IFDEQ match-digest` - Set the key’s value and expiration only if the
digest of its current value is equal to match-digest. If key doesn’t
exist - it won’t be created.
`IFDNE match-digest` - Set the key’s value and expiration only if the
digest of its current value is not equal to match-digest. If key doesn’t
exist - it will be created.
Reply update:
- If GET was not specified:
- Nil reply if either
- the key doesn’t exist and XX/IFEQ/IFDEQ was specified. The key was not
created.
- the key exists, and NX was specified or a specified
IFEQ/IFNE/IFDEQ/IFDNE condition is false. The key was not set.
- Simple string reply: OK: The key was set.
- If GET was specified, any of the following:
- Nil reply: The key didn't exist before this command (whether the key
was created or not).
- Bulk string reply: The previous value of the key (whether the key was
set or not).
### DELEX
```
DELEX key [IFEQ match-value | IFNE match-value | IFDEQ match-digest | IFDNE match-digest]
```
Conditionally removes the specified key. A key is ignored if it does not
exist.
`IFEQ match-value` - Delete the key only if its value is equal to
match-value
`IFNE match-value` - Delete the key only if its value is not equal to
match-value
`IFDEQ match-digest` - Delete the key only if the digest of its value is
equal to match-digest
`IFDNE match-digest` - Delete the key only if the digest of its value is
not equal to match-digest
Reply:
- error if key exists but holds a value that is not a string and
IFEQ/IFNE/IFDEQ/IFDNE is specified.
- (integer) 0 if not deleted (the key does not exist or a specified
IFEQ/IFNE/IFDEQ/IFDNE condition is false), or 1 if deleted.
### Notes
Added copy of xxhash repo to deps -
[version](
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||
|---|---|---|
| .. | ||
| corrupt_empty_keys.rdb | ||
| corrupt_ziplist.rdb | ||
| default.conf | ||
| encodings.rdb | ||
| hash-ziplist.rdb | ||
| hash-zipmap.rdb | ||
| list-quicklist.rdb | ||
| minimal.conf | ||
| nodefaultuser.acl | ||
| rdb-preamble.aof | ||
| scriptbackup.rdb | ||
| test_cli_hint_suite.txt | ||
| user.acl | ||
| userwithselectors.acl | ||
| zset-ziplist.rdb | ||