uriyage 46393f9819
Optimization: sdsRemoveFreeSpace to avoid realloc on noop (#11766)
In #7875 (Redis 6.2), we changed the sds alloc to be the usable allocation
size in order to:

> reduce the need for realloc calls by making the sds implicitly take over
the internal fragmentation

This change was done most sds functions, excluding `sdsRemoveFreeSpace` and
`sdsResize`, the reason is that in some places (e.g. clientsCronResizeQueryBuffer)
we call sdsRemoveFreeSpace when we see excessive free space and want to trim it.
so if we don't trim it exactly to size, the caller may still see excessive free space and
call it again and again.

However, this resulted in some excessive calls to realloc, even when there's no need
and it's gonna be a no-op (e.g. when reducing 15 bytes allocation to 13).

It turns out that a call for realloc with jemalloc can be expensive even if it ends up
doing nothing, so this PR adds a check using `je_nallocx`, which is cheap to avoid
the call for realloc.

in addition to that this PR unifies sdsResize and sdsRemoveFreeSpace into common
code. the difference between them was that sdsResize would avoid using SDS_TYPE_5,
since it want to keep the string ready to be resized again, while sdsRemoveFreeSpace
would permit using SDS_TYPE_5 and get an optimal memory consumption.
now both methods take a `would_regrow` argument that makes it more explicit.

the only actual impact of that is that in clientsCronResizeQueryBuffer we call both sdsResize
and sdsRemoveFreeSpace for in different cases, and we now prevent the use of SDS_TYPE_5 in both.

The new test that was added to cover this concern used to pass before this PR as well,
this PR is just a performance optimization and cleanup.

Benchmark:
`redis-benchmark -c 100 -t set  -d 512 -P 10  -n  100000000`
on i7-9850H with jemalloc, shows improvement from 1021k ops/sec to 1067k (average of 3 runs).
some 4.5% improvement.

Co-authored-by: Oran Agra <oran@redislabs.com>
2023-01-31 17:26:35 +02:00
..

Redis Test Suite

The normal execution mode of the test suite involves starting and manipulating local redis-server instances, inspecting process state, log files, etc.

The test suite also supports execution against an external server, which is enabled using the --host and --port parameters. When executing against an external server, tests tagged external:skip are skipped.

There are additional runtime options that can further adjust the test suite to match different external server configurations:

Option Impact
--singledb Only use database 0, don't assume others are supported.
--ignore-encoding Skip all checks for specific encoding.
--ignore-digest Skip key value digest validations.
--cluster-mode Run in strict Redis Cluster compatibility mode.
--large-memory Enables tests that consume more than 100mb

Tags

Tags are applied to tests to classify them according to the subsystem they test, but also to indicate compatibility with different run modes and required capabilities.

Tags can be applied in different context levels:

  • start_server context
  • tags context that bundles several tests together
  • A single test context.

The following compatibility and capability tags are currently used:

Tag Indicates
external:skip Not compatible with external servers.
cluster:skip Not compatible with --cluster-mode.
large-memory Test that requires more than 100mb
tls:skip Not compatible with --tls.
needs:repl Uses replication and needs to be able to SYNC from server.
needs:debug Uses the DEBUG command or other debugging focused commands (like OBJECT REFCOUNT).
needs:pfdebug Uses the PFDEBUG command.
needs:config-maxmemory Uses CONFIG SET to manipulate memory limit, eviction policies, etc.
needs:config-resetstat Uses CONFIG RESETSTAT to reset statistics.
needs:reset Uses RESET to reset client connections.
needs:save Uses SAVE or BGSAVE to create an RDB file.

When using an external server (--host and --port), filtering using the external:skip tags is done automatically.

When using --cluster-mode, filtering using the cluster:skip tag is done automatically.

When not using --large-memory, filtering using the largemem:skip tag is done automatically.

In addition, it is possible to specify additional configuration. For example, to run tests on a server that does not permit SYNC use:

./runtest --host <host> --port <port> --tags -needs:repl