In the `HRANDFIELD`, `SRANDMEMBER` and `ZRANDMEMBER` commands,
There are some strategies that could in some rare cases return an unfair random.
these cases are where s small dict happens be be hashed unevenly.
Specifically when `count*ZRANDMEMBER_SUB_STRATEGY_MUL > size`,
using `dictGetRandomKey` to randomize from a dict will result in an unfair random result.
Part two of implementing #8702 (zset), after #8887.
## Description of the feature
Replaced all uses of ziplist with listpack in t_zset, and optimized some of the code to optimize performance.
## Rdb format changes
New `RDB_TYPE_ZSET_LISTPACK` rdb type.
## Rdb loading improvements:
1) Pre-expansion of dict for validation of duplicate data for listpack and ziplist.
2) Simplifying the release of empty key objects when RDB loading.
3) Unify ziplist and listpack data verify methods for zset and hash, and move code to rdb.c.
## Interface changes
1) New `zset-max-listpack-entries` config is an alias for `zset-max-ziplist-entries` (same with `zset-max-listpack-value`).
2) OBJECT ENCODING will return listpack instead of ziplist.
## Listpack improvements:
1) Add `lpDeleteRange` and `lpDeleteRangeWithEntry` functions to delete a range of entries from listpack.
2) Improve the performance of `lpCompare`, converting from string to integer is faster than converting from integer to string.
3) Replace `snprintf` with `ll2string` to improve performance in converting numbers to strings in `lpGet()`.
## Zset improvements:
1) Improve the performance of `zzlFind` method, use `lpFind` instead of `lpCompare` in a loop.
2) Use `lpDeleteRangeWithEntry` instead of `lpDelete` twice to delete a element of zset.
## Tests
1) Add some unittests for `lpDeleteRange` and `lpDeleteRangeWithEntry` function.
2) Add zset RDB loading test.
3) Add benchmark test for `lpCompare` and `ziplsitCompare`.
4) Add empty listpack zset corrupt dump test.
Part one of implementing #8702 (taking hashes first before other types)
## Description of the feature
1. Change ziplist encoded hash objects to listpack encoding.
2. Convert existing ziplists on RDB loading time. an O(n) operation.
## Rdb format changes
1. Add RDB_TYPE_HASH_LISTPACK rdb type.
2. Bump RDB_VERSION to 10
## Interface changes
1. New `hash-max-listpack-entries` config is an alias for `hash-max-ziplist-entries` (same with `hash-max-listpack-value`)
2. OBJECT ENCODING will return `listpack` instead of `ziplist`
## Listpack improvements:
1. Support direct insert, replace integer element (rather than convert back and forth from string)
3. Add more listpack capabilities to match the ziplist ones (like `lpFind`, `lpRandomPairs` and such)
4. Optimize element length fetching, avoid multiple calculations
5. Use inline to avoid function call overhead.
## Tests
1. Add a new test to the RDB load time conversion
2. Adding the listpack unit tests. (based on the one in ziplist.c)
3. Add a few "corrupt payload: fuzzer findings" tests, and slightly modify existing ones.
Co-authored-by: Oran Agra <oran@redislabs.com>
Reduce dict struct memory overhead
on 64bit dict size goes down from jemalloc's 96 byte bin to its 56 byte bin.
summary of changes:
- Remove `privdata` from callbacks and dict creation. (this affects many files, see "Interface change" below).
- Meld `dictht` struct into the `dict` struct to eliminate struct padding. (this affects just dict.c and defrag.c)
- Eliminate the `sizemask` field, can be calculated from size when needed.
- Convert the `size` field into `size_exp` (exponent), utilizes one byte instead of 8.
Interface change: pass dict pointer to dict type call back functions.
This is instead of passing the removed privdata field. In the future if
we'd like to have private data in the callbacks we can extract it from
the dict type. We can extend dictType to include a custom dict struct
allocator and use it to allocate more data at the end of the dict
struct. This data can then be used to store private data later acccessed
by the callbacks.
due to a copy-paste bug, it used to reply with null response rather than empty array.
this commit includes new tests that are looking at the RESP response directly in
order to be able to tell the difference between them.
Co-authored-by: Oran Agra <oran@redislabs.com>
1. Add one key-value pair to myhash, which the length of key and value both less than hash-max-ziplist-value, for example:
>hset myhash key value
2. Then execute the following command
>hsetnx myhash key value1 (the length greater than hash-max-ziplist-value)
3. This will add nothing, but the code type of "myhash" changed from ziplist to dict even there are only one key-value pair in "myhash", and both of them less than hash-max-ziplist-value.
SRANDMEMBER with negative count (non unique) can return the same member
multiple times, and the order of elements in the returned collection matters.
For these reasons returning a RESP3 Set type is not valid for the negative
count, but also not really valid for the positive (unique) variant either (the
command returns an array of random picks, not a set)
This PR also contains a minor optimization for SRANDMEMBER, HRANDFIELD,
and ZRANDMEMBER, to avoid the temporary dict from being rehashed while it grows.
Co-authored-by: Oran Agra <oran@redislabs.com>
Avoids memmove and reallocs when replacing a ziplist element of the
same encoded size as the new value.
Affects HSET, HINRBY, HINCRBYFLOAT (via hashTypeSet) and LSET (via
quicklistReplaceAtIndex).
It is inefficient to repeatedly pick a single random element from a
ziplist.
For CASE4, which is when the user requested a low number of unique
random picks from the collectoin, we used thta pattern.
Now we use a different algorithm that picks unique elements from a
ziplist, and guarentee no duplicate but doesn't provide random order
(which is only needed in the non-unique random picks case)
Unrelated changes:
* change ziplist count and indexes variables to unsigned
* solve compilation warnings about uninitialized vars in gcc 10.2
Co-authored-by: xinluton <xinluton@qq.com>
Changes to HRANDFIELD and ZRANDMEMBER:
* Fix risk of OOM panic when client query a very big negative count (avoid allocating huge temporary buffer).
* Fix uneven random distribution in HRANDFIELD with negative count (wasn't using dictGetFairRandomKey).
* Add tests to check an even random distribution (HRANDFIELD, SRANDMEMBER, ZRANDMEMBER).
Co-authored-by: Oran Agra <oran@redislabs.com>
New commands:
`HRANDFIELD [<count> [WITHVALUES]]`
`ZRANDMEMBER [<count> [WITHSCORES]]`
Algorithms are similar to the one in SRANDMEMBER.
Both return a simple bulk response when no arguments are given, and an array otherwise.
In case values/scores are requested, RESP2 returns a long array, and RESP3 a nested array.
note: in all 3 commands, the only option that also provides random order is the one with negative count.
Changes to SRANDMEMBER
* Optimization when count is 1, we can use the more efficient algorithm of non-unique random
* optimization: work with sds strings rather than robj
Other changes:
* zzlGetScore: when zset needs to convert string to double, we use safer memcpy (in
case the buffer is too small)
* Solve a "bug" in SRANDMEMBER test: it intended to test a positive count (case 3 or
case 4) and by accident used a negative count
Co-authored-by: xinluton <xinluton@qq.com>
Co-authored-by: Oran Agra <oran@redislabs.com>
Fix wrong server dirty increment in
* spopWithCountCommand
* hsetCommand
* ltrimCommand
* pfaddCommand
Some didn't increment the amount of fields (just one per command).
Others had excessive increments.
If RESTORE passes successfully with full sanitization, we can't affort
to crash later on assertion due to duplicate records in a hash when
converting it form ziplist to dict.
This means that when doing full sanitization, we must make sure there
are no duplicate records in any of the collections.
When loading an encoded payload we will at least do a shallow validation to
check that the size that's encoded in the payload matches the size of the
allocation.
This let's us later use this encoded size to make sure the various offsets
inside encoded payload don't reach outside the allocation, if they do, we'll
assert/panic, but at least we won't segfault or smear memory.
We can also do 'deep' validation which runs on all the records of the encoded
payload and validates that they don't contain invalid offsets. This lets us
detect corruptions early and reject a RESTORE command rather than accepting
it and asserting (crashing) later when accessing that payload via some command.
configuration:
- adding ACL flag skip-sanitize-payload
- adding config sanitize-dump-payload [yes/no/clients]
For now, we don't have a good way to ensure MIGRATE in cluster resharding isn't
being slowed down by these sanitation, so i'm setting the default value to `no`,
but later on it should be set to `clients` by default.
changes:
- changing rdbReportError not to `exit` in RESTORE command
- adding a new stat to be able to later check if cluster MIGRATE isn't being
slowed down by sanitation.
Syntax:
COPY <key> <new-key> [DB <dest-db>] [REPLACE]
No support for module keys yet.
Co-authored-by: tmgauss
Co-authored-by: Itamar Haber <itamar@redislabs.com>
Co-authored-by: Oran Agra <oran@redislabs.com>
looks like each platform implements long double differently (different bit count)
so we can't save them as binary, and we also want to avoid creating a new RDB
format version, so we save these are hex strings using "%La".
This commit includes a change in the arguments of ld2string to support this.
as well as tests for coverage and short reads.
coded by @guybe7
The string representation of `long double` may take
up to ~5000 chars (see PR #3745).
Before this fix HINCRBYFLOAT would never overflow (since
the string could not exceed 256 chars). Now it can.
This is the first step towards getting rid of HMSET which is a command
that does not make much sense once HSET is variadic, and has a saner
return value.
During the refactoring needed for lazy free, specifically the conversion
of t_hash from struct robj to plain SDS strings, HINCRBFLOAT was
accidentally moved away from long doubles to doubles for internal
processing of increments and formatting.
The diminished precision created more obvious artifacts in the way small
numbers are formatted once we convert from decimal number in radix 10 to
double and back to its string in radix 10.
By using more precision, we now have less surprising results at least
with small numbers like "1.23", exactly like in the previous versions of
Redis.
See issue #2846.
