mirror of
https://codeberg.org/redict/redict.git
synced 2025-01-22 08:08:53 -05:00
2753429c99
### Description A mechanism for disconnecting clients when the sum of all connected clients is above a configured limit. This prevents eviction or OOM caused by accumulated used memory between all clients. It's a complimentary mechanism to the `client-output-buffer-limit` mechanism which takes into account not only a single client and not only output buffers but rather all memory used by all clients. #### Design The general design is as following: * We track memory usage of each client, taking into account all memory used by the client (query buffer, output buffer, parsed arguments, etc...). This is kept up to date after reading from the socket, after processing commands and after writing to the socket. * Based on the used memory we sort all clients into buckets. Each bucket contains all clients using up up to x2 memory of the clients in the bucket below it. For example up to 1m clients, up to 2m clients, up to 4m clients, ... * Before processing a command and before sleep we check if we're over the configured limit. If we are we start disconnecting clients from larger buckets downwards until we're under the limit. #### Config `maxmemory-clients` max memory all clients are allowed to consume, above this threshold we disconnect clients. This config can either be set to 0 (meaning no limit), a size in bytes (possibly with MB/GB suffix), or as a percentage of `maxmemory` by using the `%` suffix (e.g. setting it to `10%` would mean 10% of `maxmemory`). #### Important code changes * During the development I encountered yet more situations where our io-threads access global vars. And needed to fix them. I also had to handle keeps the clients sorted into the memory buckets (which are global) while their memory usage changes in the io-thread. To achieve this I decided to simplify how we check if we're in an io-thread and make it much more explicit. I removed the `CLIENT_PENDING_READ` flag used for checking if the client is in an io-thread (it wasn't used for anything else) and just used the global `io_threads_op` variable the same way to check during writes. * I optimized the cleanup of the client from the `clients_pending_read` list on client freeing. We now store a pointer in the `client` struct to this list so we don't need to search in it (`pending_read_list_node`). * Added `evicted_clients` stat to `INFO` command. * Added `CLIENT NO-EVICT ON|OFF` sub command to exclude a specific client from the client eviction mechanism. Added corrosponding 'e' flag in the client info string. * Added `multi-mem` field in the client info string to show how much memory is used up by buffered multi commands. * Client `tot-mem` now accounts for buffered multi-commands, pubsub patterns and channels (partially), tracking prefixes (partially). * CLIENT_CLOSE_ASAP flag is now handled in a new `beforeNextClient()` function so clients will be disconnected between processing different clients and not only before sleep. This new function can be used in the future for work we want to do outside the command processing loop but don't want to wait for all clients to be processed before we get to it. Specifically I wanted to handle output-buffer-limit related closing before we process client eviction in case the two race with each other. * Added a `DEBUG CLIENT-EVICTION` command to print out info about the client eviction buckets. * Each client now holds a pointer to the client eviction memory usage bucket it belongs to and listNode to itself in that bucket for quick removal. * Global `io_threads_op` variable now can contain a `IO_THREADS_OP_IDLE` value indicating no io-threading is currently being executed. * In order to track memory used by each clients in real-time we can't rely on updating these stats in `clientsCron()` alone anymore. So now I call `updateClientMemUsage()` (used to be `clientsCronTrackClientsMemUsage()`) after command processing, after writing data to pubsub clients, after writing the output buffer and after reading from the socket (and maybe other places too). The function is written to be fast. * Clients are evicted if needed (with appropriate log line) in `beforeSleep()` and before processing a command (before performing oom-checks and key-eviction). * All clients memory usage buckets are grouped as follows: * All clients using less than 64k. * 64K..128K * 128K..256K * ... * 2G..4G * All clients using 4g and up. * Added client-eviction.tcl with a bunch of tests for the new mechanism. * Extended maxmemory.tcl to test the interaction between maxmemory and maxmemory-clients settings. * Added an option to flag a numeric configuration variable as a "percent", this means that if we encounter a '%' after the number in the config file (or config set command) we consider it as valid. Such a number is store internally as a negative value. This way an integer value can be interpreted as either a percent (negative) or absolute value (positive). This is useful for example if some numeric configuration can optionally be set to a percentage of something else. Co-authored-by: Oran Agra <oran@redislabs.com> |
||
|---|---|---|
| .. | ||
| assets | ||
| cluster | ||
| helpers | ||
| integration | ||
| modules | ||
| sentinel | ||
| support | ||
| tmp | ||
| unit | ||
| instances.tcl | ||
| README.md | ||
| test_helper.tcl | ||
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. |
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_servercontexttagscontext 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. |
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). |
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 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.
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