Sharing latency: File can be shared, giving you shared memory between processes and can be more 10x lower latency than using a Socket over loopback.Performance: Memory-mapped Files are way faster than the standard ones.Merits of the memory-mapped file are as follows: But with these merits, also do comes demerits which are shown below: ISRO CS Syllabus for Scientist/Engineer Examīy far we have studied what and why we use memory-mapped files alongside have seen the implementation too.ISRO CS Original Papers and Official Keys.GATE CS Original Papers and Official Keys.DevOps Engineering - Planning to Production.Python Backend Development with Django(Live).Android App Development with Kotlin(Live).Full Stack Development with React & Node JS(Live).Java Programming - Beginner to Advanced.Data Structure & Algorithm-Self Paced(C++/JAVA).Data Structures & Algorithms in JavaScript.Data Structure & Algorithm Classes (Live).The key performance boost comes from the combination with mvec, which can then use data on file as efficiently as in memory. ![]() That is why the output below consists of two sections - one with C-level support, and one in pure Tcl.ĭon't put too much emphasis on speed differences as shown below. One of the nice things about "mmap" is that it can be faked entirely in pure Tcl (by reading the entire file on first access). The code will be moved into a context and namespace of its own when the dust has settled a bit more.īelow are some examples. This demo includes the C code for mmap (and a few more pieces), with a binary build (just Linux for now). JOLT stands for JC's Own Little Toolbox - it's a context I use to try out new things, especially when mixing Tcl and C and exploring possibilities. When compiled as C extension, "mmap" is part of JOLT. This is the "vkit" project as described elsewhere and is work in progress. The combination mvec+mmap makes it possible to implement high-performance vector storage. ![]() The "mmap" command is particular in the sense that "mvec" is special-cased to work with it if present (see "mvec.README"). Even end-of-line translations and end-of-file markers are totally ignored. Keep in mind that mmap is for binary data - it's 100% ignorant of Unicode. A simple way to do this, is to store the channel identifier in a variable, and never use that variable in any other way than as first arg to "mmap". That means that you need to be careful to rarely lose the dual-object representation. Accessing data in this way is extremely efficient, but setting up / tearing down such a mapping is not that cheap. Trivial, eh? You can throw away the "read" command now :)Īctually, things are slightly more complex. The result is a 17-byte string (byte array, to be precise), as found at offset 123 in the file. The second call is the one to fetch a particular byte range: set offset 123 This returns the file size (and sets up the mmap as dual representation). Sockets cannot be used, the file descriptor must be mappable (which is whatever the OS considers acceptable).Īfter that, you only need to deal with two call variations to "mmap": set filesize ![]() What you need is an open file in the form of a Tcl "channel" descriptor. The interface is almost hidden, it's very easy to forget it exists (it's also easy to cause "shimmering" and lose most of the speed advantage). ![]() Using data in such a way takes maximum advantage of virtual memory (VM). This demo illustrates an experimental "mmap" command and datatype for Tcl, which provides efficient access to files by mapping them into memory. The "mmap" command for memory mapping is now part of the mvector package in CritLib.
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