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What is a thread cache?
TCMalloc is a memory allocator designed as an alternative to the system default allocator that has the following characteristics: Fast, uncontended allocation and deallocation for most objects. Objects are cached, depending on mode, either per-thread, or per-logical-CPU.
What is thread cache in MySQL?
In the MySQL 5.7 manual, I read that the thread cache has a size determined by the thread_cache_size system variable. The default value is 0 (no caching), which causes a thread to be set up for each new connection and disposed of when the connection terminates.
What are threads in MySQL?
The MySQL server creates the following threads: Connection manager threads handle client connection requests on the network interfaces that the server listens to. On all platforms, one manager thread handles TCP/IP connection requests. On Unix, this manager thread also handles Unix socket file connection requests.
In a shared-cache machine, multiple processors or concur- rent threads share a single cache. When a shared physical memory is used as a cache for disk memory, as is supported by virtual memory, standard shared-memory multiproces- sors can also be treated as shared-cache machines.
What is false sharing in distributed system?
False sharing occurs when processors in a shared-memory parallel system make references to different data objects within the same coherence block (cache line or page), thereby inducing “unnecessary” coherence operations.
How many threads can MySQL handle?
The maximum number of threads per group is 4096 (or 4095 on some systems where one thread is used internally). The thread pool separates connections and threads, so there is no fixed relationship between connections and the threads that execute statements received from those connections.
How do I see what MySQL threads are running?
The ‘SHOW processlist’ command can be used to display the running thread related to only your MySQL account. We can see almost all running threads if we have process privileges. It shows which threads are running.
What causes false sharing?
False sharing occurs when threads on different processors modify variables that reside on the same cache line. If the processor stores a cache line marked as ‘S’, the cache line is marked as ‘Modified’ and all other processors are sent an ‘Invalid’ cache line message.
What is a ” thread ” in thread _ cache _ size?
On *nix, a MySQL thread is a relatively heavy-weight “process”. You can see the “processes” in top or ps. For Windows, thread_cache_size = 0 is OK. This is because threading is done differently. On *nix, thread_cache_size should be a modest number, say, 20. It is the maximum number of unused processes to keep open.
When to change the thread cache size in MySQL?
The thread_cache_size can be changed in a live environment. So this allows you to set the variable then monitor the status value of the “Threads_created” (see above to get value). If this continues to increment in value then continue to raise the thread_cache_size.
What is the status of threads in MySQL?
The STATUS values of Threads_cached/connected/created/running give a peak into whether the VARIABLE thread_cache_size needs tuning. Threads_created/Uptime is how fast a new process is being created because the cache is too small. Recommend keeping this under 3/second.
What’s the uptime of a thread in MySQL?
Threads_created/Uptime is how fast a new process is being created because the cache is too small. Recommend keeping this under 3/second. Thanks for contributing an answer to Database Administrators Stack Exchange!