WEBVTT 00:00.230 --> 00:04.340 Hey everyone, and welcome to the Knowledge Portal Video series. 00:04.340 --> 00:11.030 So today we'll be speaking about an important topic which basically rules our Internet life behind the 00:11.030 --> 00:11.660 scenes. 00:11.660 --> 00:14.660 And the topic name is called as caching. 00:14.660 --> 00:19.010 Now, I'm very sure that most of you might have heard about this word. 00:19.010 --> 00:27.830 Caching and caching proves to be a great importance as far as the Http protocol and browsing is concerned. 00:27.860 --> 00:32.510 So let's go ahead and understand the basics about caching. 00:34.160 --> 00:41.240 So with my favorite example that we take every time you have a client and you have a web server. 00:41.570 --> 00:44.450 So a client basically sends a request. 00:44.450 --> 00:53.900 So in our case it is get request on my C dot PNG and the web server responds back with the. 00:55.140 --> 00:55.890 PNG file. 00:56.370 --> 01:00.930 Now this is a very simple Http request and Http response. 01:00.960 --> 01:09.000 Now the problem that arises over here is what happens if the client sends the same get request ten times 01:09.000 --> 01:11.380 like he keeps refreshing the page. 01:11.400 --> 01:20.190 So this get request will be sent to the server ten times and the server will have to process and send 01:20.190 --> 01:22.050 the response ten times again. 01:23.030 --> 01:30.830 And basically this might not seem to be a big issue, but when you talk about big websites like Facebook, 01:30.860 --> 01:39.200 Amazon or any big websites you can consider, they have like millions of users who visit their website 01:39.200 --> 01:39.830 every day. 01:39.830 --> 01:44.840 And most of us, we refresh the page like, how many of you open Facebook? 01:44.870 --> 01:48.610 Like many of you open like ten times a day, 15 times a day. 01:48.620 --> 01:56.420 And basically what happens, like there are certain static contents like your DP picture or DP of your 01:56.420 --> 01:59.060 friends that will not change often. 01:59.060 --> 02:06.890 So the more you open, the more same requests will be sent to the web server and the more web server 02:06.890 --> 02:09.410 will have to process the same response back. 02:09.410 --> 02:12.550 So this is where the problem arises. 02:12.560 --> 02:19.190 And in order to solve this, there needs to be a basic caching mechanism and this is something which 02:19.190 --> 02:20.500 is implemented. 02:20.510 --> 02:30.360 So what happens in cache mechanism is there is a middleware server, so this middleware server is responsible 02:30.360 --> 02:31.620 for caching. 02:31.620 --> 02:38.910 So now what happens is the client sends a request, The request. 02:39.500 --> 02:44.780 Is forwarded to the web server with a cache in middle. 02:45.230 --> 02:51.740 Now in the response, the web server responds back to the cache and the cache. 02:53.290 --> 02:57.130 Sends the response back to the client. 02:57.250 --> 03:02.380 Now let's look it in a Http way. 03:02.740 --> 03:09.700 So the client sends a request call as get on my dot PNG. 03:09.970 --> 03:13.210 The request is received on the cache server. 03:13.540 --> 03:18.640 Cache server will send the same request to the web server. 03:18.670 --> 03:27.910 Now since this is a get request on my c dot PNG, the web server will respond back with a file. 03:27.910 --> 03:31.030 So this is the my c dot png file. 03:31.480 --> 03:37.510 Now what cache server will do is cache server has its own storage. 03:38.290 --> 03:41.080 So what cache server will do? 03:41.110 --> 03:50.530 Cache server will store this file my c dot png within this storage and then it will reply back to the 03:50.530 --> 03:52.310 client with the file. 03:53.120 --> 03:54.680 Okay, so. 03:55.660 --> 04:05.050 Now, what would happen is if the client decides to refresh the page, then what would happen is or 04:05.050 --> 04:07.330 if there are multiple same requests. 04:07.360 --> 04:12.830 Now, we already know that the cache server has stored the MC dot PNG file. 04:12.880 --> 04:20.070 In that case, if the user decides to refresh the page, you have, you have get on MC dot PNG. 04:20.080 --> 04:23.170 So user is sending the same request again. 04:23.200 --> 04:25.510 So now what cache server will do? 04:25.540 --> 04:33.440 Cache server knows that there is already a file called as MC dot PNG within its local store. 04:33.460 --> 04:35.200 So the. 04:36.460 --> 04:40.070 Castro will respond with the same file. 04:40.090 --> 04:48.610 So in this case, what happened was the cache server did not send the request to the client or to the 04:48.610 --> 04:49.590 web server. 04:49.600 --> 04:52.900 It responded back with the local cache. 04:53.650 --> 05:02.950 Now, this specific local cache can be a hard disk drive or it can be a memory also to fasten the things 05:02.950 --> 05:03.310 up. 05:03.310 --> 05:06.290 So let's look into how that would work. 05:06.310 --> 05:15.160 Now this local cache can be a dedicated server, which an organization can have, or it can be a software 05:15.160 --> 05:16.570 based appliance also. 05:16.570 --> 05:20.260 So most of the browsers does have local cache. 05:20.260 --> 05:25.450 So this is mostly a software appliance as far as the browsers are concerned. 05:25.540 --> 05:27.910 So let's look into how that would work. 05:29.930 --> 05:33.500 So I have a Firefox browser. 05:33.500 --> 05:40.460 So if you go into about colon cache, this will basically tell you all the caching related information 05:40.460 --> 05:42.380 which the browser keeps. 05:42.380 --> 05:46.700 So you can consider this as a software appliance of the browser. 05:46.820 --> 05:50.510 Now there are two important things to remember is. 05:51.530 --> 05:57.920 That the cash can be stored in memory and the cash can be stored in disk. 05:57.950 --> 06:03.480 Now, if you store it in memory, then definitely the it will be much more faster. 06:03.500 --> 06:04.460 However. 06:05.820 --> 06:09.870 Bisque is also quite fast, but not as fast as memory. 06:09.870 --> 06:17.370 But overall, retrieving files from disk is much, much more faster than actually contacting the web 06:17.370 --> 06:19.500 server and fetching the files. 06:19.620 --> 06:26.280 Now, if you look into the disk, it basically tells you how many entries are part of the cache. 06:26.310 --> 06:32.940 It also tells you about the storage and the storage location where the cache is stored. 06:33.150 --> 06:40.200 So now if you go to list cache entries over here, it will basically tells you what are the files which 06:40.200 --> 06:41.730 are being cached over here. 06:44.140 --> 06:54.010 Now, along with that it tells you about let's show it talks about the fetch count basically tells on 06:54.010 --> 06:57.100 how many times the item has been fetched. 06:57.130 --> 07:03.370 It talks about the expiry time of that specific cache value. 07:03.580 --> 07:10.240 So if you look into this specific entry, so this is something related to a PNG file. 07:10.330 --> 07:13.870 Stars dot PNG, which is a 1 to 73 bytes. 07:13.990 --> 07:16.780 It has been fetched two times in total. 07:16.780 --> 07:18.510 And for how many time? 07:18.520 --> 07:20.500 How much time it will be cached. 07:20.590 --> 07:30.310 So it has the first retrieval time was 2410, 2017 and it has been actually cached for a good amount 07:30.310 --> 07:30.850 of time. 07:30.850 --> 07:31.480 You see. 07:31.900 --> 07:40.150 11 one 2027 That is actually an amazing caching amount of time. 07:40.150 --> 07:48.590 So generally files are cached for like one year, but this seems to be quite good enough anyways. 07:48.590 --> 07:51.110 So let's do one thing. 07:52.580 --> 07:55.670 What we'll be doing is let's open a file. 07:56.030 --> 08:01.220 So Dexter Labs dot in, slash my c dot jpg. 08:01.610 --> 08:09.530 So this is basically a image file which is retrieved from Dexter Labs dot slash my C. 08:09.680 --> 08:16.910 So now if I keep refreshing the page question is should a browser send a request to the web server every 08:16.910 --> 08:20.380 time and expect a response that would be much more slower? 08:20.390 --> 08:27.530 So in this case, what the browser will do, a browser will basically. 08:29.430 --> 08:31.560 Cached image file. 08:32.310 --> 08:38.400 So now what would happen is if you look here, the fetch count is 13. 08:38.400 --> 08:41.160 So this basically means that. 08:42.190 --> 08:50.310 This file is already cached and it has been fetched for 13 times in total. 08:50.320 --> 08:56.050 It talks about the last modified time and it talks about the expires time. 08:56.050 --> 09:00.280 Like when will this file expire from cache? 09:00.940 --> 09:10.210 So next time, even when you refresh the page, the chances are that it will be retrieved from the browser 09:10.210 --> 09:17.170 cache and the get request will not be sent to the server directly. 09:17.170 --> 09:25.960 So this is it about the high level overview about what the caching is all about in Http protocol. 09:25.960 --> 09:29.830 Now, definitely one last thing that caching does bring. 09:29.830 --> 09:33.970 If you note it does bring a good amount of benefits. 09:33.970 --> 09:40.360 Now one of the very good benefits is that it reduces the overhead of the server resources. 09:40.390 --> 09:47.180 Now, since the browser is retrieving the file from the cache, the server, the web server does not 09:47.180 --> 09:50.930 have to process the response and send it back to the client. 09:50.930 --> 09:54.110 So it basically reduces the overall overhead. 09:54.470 --> 09:57.920 Second is, it decreases the network bandwidth. 09:57.920 --> 10:06.260 Now every time a user refreshes the page and if the request is sent to the web server, then the overall 10:06.260 --> 10:09.260 network bandwidth will be tremendously high. 10:09.260 --> 10:18.920 And since now a browser retrieves it from the local cache, the network is not congested and third pages 10:18.920 --> 10:23.060 are loaded much more faster since the entries are cached within the. 10:24.780 --> 10:27.260 Desktop or within the server itself. 10:27.270 --> 10:30.870 So these are some of the benefits of caching. 10:30.870 --> 10:38.610 In the upcoming lectures, we will be speaking in great detail related to caching and caching related 10:38.610 --> 10:39.330 headers. 10:40.080 --> 10:42.480 So this is it about this lecture. 10:42.480 --> 10:48.300 If you have any doubts suggestions, feel free to connect us at Twitter, Facebook or LinkedIn or mail 10:48.300 --> 10:50.580 us at instructors at KP Labs. 10:51.030 --> 10:52.320 Thanks for watching.