This code was extracted from @oranagra PR #3223 and modified in order
to provide only certain amounts of information compared to the original
code. It was also moved from DEBUG to the newly introduced MEMORY
command. Thanks to Oran for the implementation and the PR.
It implements detailed memory usage stats that can be useful in both
provisioning and troubleshooting memory usage in Redis.
For most tasks, we need the memory estimation to be O(1) by default.
This commit also implements an initial MEMORY command.
Note that objectComputeSize() takes the number of samples to check as
argument, so MEMORY should be able to get the sample size as option
to make precision VS CPU tradeoff tunable.
Related to: PR #3223.
It is possible to get better results by using the pool like in the LRU
case. Also from tests during the morning I believe the current
implementation has issues in the frequency decay function that should
decrease the counter at periodic intervals.
strict_strtoll() has a bug that reports the empty string as ok and
parses it as zero.
Apparently nobody ever replaced this old call with the faster/saner
string2ll() which is used otherwise in the rest of the Redis core.
This commit close#3333.
Should be much faster, and regardless, the code is more obvious now
compared to generating a string just to get the return value of the
ll2stirng() function.
This replaces individual ziplist vs. linkedlist representations
for Redis list operations.
Big thanks for all the reviews and feedback from everybody in
https://github.com/antirez/redis/pull/2143
In order to make sure every object has its own private LRU counter, when
maxmemory is enabled tryObjectEncoding() does not use the pool of shared
integers. However when the policy is not LRU-based, it does not make
sense to do so, and it is much better to save memory using shared
integers.
Previously, the command definition for the OBJECT command specified
a minimum of two args (and that it was variadic), which meant that
if you sent this:
OBJECT foo
When cluster was enabled, it would result in an assertion/SEGFAULT
when Redis was attempting to extract keys.
It appears that OBJECT is not variadic, and only ever takes 3 args.
https://gist.github.com/michael-grunder/25960ce1508396d0d36a
All the Redis functions that need to modify the string value of a key in
a destructive way (APPEND, SETBIT, SETRANGE, ...) require to make the
object unshared (if refcount > 1) and encoded in raw format (if encoding
is not already REDIS_ENCODING_RAW).
This was cut & pasted many times in multiple places of the code. This
commit puts the small logic needed into a function called
dbUnshareStringValue().
For testing purposes it is handy to have a very high resolution of the
LRU clock, so that it is possible to experiment with scripts running in
just a few seconds how the eviction algorithms works.
This commit allows Redis to use the cached LRU clock, or a value
computed on demand, depending on the resolution. So normally we have the
good performance of a precomputed value, and a clock that wraps in many
days using the normal resolution, but if needed, changing a define will
switch behavior to an high resolution LRU clock.
We are sure the string is large, since when the sds optimization branch
is entered it means that it was not possible to encode it as EMBSTR for
size concerns.
When no encoding is possible, at least try to reallocate the sds string
with one that does not waste memory (with free space at the end of the
buffer) when the string is large enough.
We are sure that a string that is longer than 21 chars cannot be
represented by a 64 bit signed integer, as -(2^64) is 21 chars:
strlen(-18446744073709551616) => 21
Thanks to @run and @badboy for spotting this.
Triva: clang was not able to provide me a warning about that when
compiling.
This closes#1024 and #1207, committing the change myself as the pull
requests no longer apply cleanly after other changes to the same
function.
Previously two string encodings were used for string objects:
1) REDIS_ENCODING_RAW: a string object with obj->ptr pointing to an sds
stirng.
2) REDIS_ENCODING_INT: a string object where the obj->ptr void pointer
is casted to a long.
This commit introduces a experimental new encoding called
REDIS_ENCODING_EMBSTR that implements an object represented by an sds
string that is not modifiable but allocated in the same memory chunk as
the robj structure itself.
The chunk looks like the following:
+--------------+-----------+------------+--------+----+
| robj data... | robj->ptr | sds header | string | \0 |
+--------------+-----+-----+------------+--------+----+
| ^
+-----------------------+
The robj->ptr points to the contiguous sds string data, so the object
can be manipulated with the same functions used to manipulate plan
string objects, however we need just on malloc and one free in order to
allocate or release this kind of objects. Moreover it has better cache
locality.
This new allocation strategy should benefit both the memory usage and
the performances. A performance gain between 60 and 70% was observed
during micro-benchmarks, however there is more work to do to evaluate
the performance impact and the memory usage behavior.
