What is epoll used for?

epoll is a Linux kernel system call for a scalable I/O event notification mechanism, first introduced in version 2.5. 44 of the Linux kernel. Its function is to monitor multiple file descriptors to see whether I/O is possible on any of them.

Table of Contents

What is an epoll event?

epoll stands for event poll and is a Linux specific construct. It allows for a process to monitor multiple file descriptors and get notifications when I/O is possible on them. It allows for both edge-triggered as well as level-triggered notifications.

What is epoll socket?

epoll_ctl() is a control function that allows us to add descriptors to a watch set, remove descriptors from a watch set, or reconfigure file descriptors already in the watch set. epoll_wait() waits for I/O events on the watch set, blocking the calling thread until one or more events are detected.

How do you read epoll?

It Improves With Listening

Practice listening well in everyday conversations. Really pay attention to what the other person is saying.
Tune in to feelings as well as story. When a friend tells you about something, try to imagine how he or she might have felt.
Take time to listen to someone in depth.

Why epoll is faster than select?

The main difference between epoll and select is that in select() the list of file descriptors to wait on only exists for the duration of a single select() call, and the calling task only stays on the sockets’ wait queues for the duration of a single call.

What is poll and epoll?

Both of them potentially trigger on a single event. However, with poll, the user then has no choice but to iterate thru the entire list submitted to find the events, whereas with epoll you get a list returned containing only the actual events. This means if the server is very busy, there is no advantage to epoll.

How use epoll Linux?

Step 1: Create epoll file descriptor. First I’ll go through the process of just creating and closing an epoll instance.
Step 2: Add file descriptors for epoll to watch. The next thing to do is tell epoll what file descriptors to watch and what kinds of events to watch for.
Step 3: Profit. That’s right!

What is the difference between poll and epoll?

What is select poll epoll?

Unlike select and poll both of which only provide one API, epoll is not a single API but a group of 3 APIs. epoll_create and epoll_add are called to set up the epoll instance while epoll_wait can be called in a loop to constantly wait on the fds added by epoll_add . The complexity of the inner loop is O(ready fds) .

What is epoll and Kqueue?

Kqueue allows one to batch modify watcher states and to retrieve watcher states in a single system call. With epoll, you have to call a system call for every modification. Kqueue also allows one to watch for things like filesystem changes and process state changes, epoll is limited to socket/pipe I/O only.

What is poll epoll?

Why is epoll better than select?

What is Linux Io_uring?

io_uring (previously known as aioring) is a Linux kernel system call interface for storage device asynchronous I/O operations addressing performance issues with similar interfaces provided by functions like read() / write() or aio_read() / aio_write() etc. for operations on data accessed by file descriptors.

Is epoll faster?

So using epoll really is a lot faster once you have more than 10 or so file descriptors to monitor.

How does Io_uring work?

Interface. Internally it works by creating two buffers dubbed as “queue rings” (circular buffers) for storage of submission and completion of I/O requests (for storage devices, submission queue (SQ) and completion queue (CQ) respectively).

What is Liburing?

liburing provides helpers to setup and teardown io_uring instances, and also a simplified interface for applications that don’t need (or want) to deal with the full kernel side implementation.

What is Linux io_uring?

What is O_direct?

O_DIRECT is a flag passed when a file is opened. It instructs to bypass page cache and perform any IO operations directly against storage. So, the buffers in the application space are flushed directly to disk, without copying the data into page cache first and waiting for the kernel to schedule write-back operations.

What is Iov_base?

void *iov_base. Contains the address of a buffer. size_t iov_len. Contains the length of the buffer.

What is Innodb_flush_method O_direct?

To apply direct I/O only to InnoDB file operations rather than the whole file system, set innodb_flush_method = O_DIRECT . With this setting, InnoDB calls directio() instead of fcntl() for I/O to data files (not for I/O to log files).

What is OS page cache?

The operating system keeps a page cache in otherwise unused portions of the main memory (RAM), resulting in quicker access to the contents of cached pages and overall performance improvements. A page cache is implemented in kernels with the paging memory management, and is mostly transparent to applications.

What is an Iovec?

Data Type: struct iovec. The iovec structure describes a buffer. It contains two fields: void *iov_base. Contains the address of a buffer.

What is Iovec in Linux?

The struct iovec defines one vector element. Normally, this structure is used as an array of multiple elements. For each transfer element, the pointer member iov_base points to a buffer that is receiving data for readv or is transmitting data for writev.

How can I improve my InnoDB performance?

innodb_thread_concurrency: With improvements to the InnoDB engine, it is recommended to allow the engine to control the concurrency by keeping it to default value (which is zero). If you see concurrency issues, you can tune this variable. A recommended value is 2 times the number of CPUs plus the number of disks.

What is Innodb_flush_log_at_trx_commit?

The innodb_flush_log_at_trx_commit system variable configures how often the transactions are flushed to the redo log: When it is set to 0, nothing is done on commit; rather the log buffer is written and flushed to the InnoDB redo log once a second.

What is epoll used for?