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Time To First Byte (TTFB) is a measurement used as an indication of the responsiveness of a webserver or other network resource. TTFB measures the duration from the user or client making an HTTP request to the first byte of the page being received by the client's browser. This time is made up of the socket connection time, the time taken to send the HTTP request, and the time taken to get the first byte of the page. Although sometimes misunderstood as a post-DNS calculation, the original calculation of TTFB in networking always includes network latency in measuring the time it takes for a resource to begin loading. Often, a smaller (faster) TTFB size is seen as a benchmark of a well-configured server application. For example, a lower Time To First Byte could point to fewer dynamic calculations being performed by the webserver, although this is often due to caching at either the DNS, server, or application level. More commonly, a very low TTFB is observed with statically served web pages, while larger TTFB is often seen with larger, dynamic data requests being pulled from a database. ==Uses in web development== Time To First Byte is important to a webpage since it indicates pages that load slowly due to server-side calculations that might be better served as client side scripting. Often this includes simple scripts and calculations like transitioning images that aren't gifs and are transitioned using Javascript to modify their transparency levels. This can often speed up a website by downloading multiple smaller images through sockets instead of one large image. However this technique is more intensive on the client's computer and on older PCs can slow the webpage down when actually rendering. Time To First Byte is so important that some webpages have forgone eager loading for lazy loading in an attempt to make their content appear to load faster. This is helpful with webpages that have many images and large amounts of data. However, there are several reasons that TTFB can be high: # database requests are fast but often require post-query logic to format the data for the end user; # Application Programming Interfaces used on the server-side can increase overall response time, as is common in Restful APIs that process large amounts of data from a database. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Time To First Byte」の詳細全文を読む スポンサード リンク
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