Minecraft Forums

So i have alot of lag in minecraft(mostly breaking blocks then they reappear again, lag when hitting mobs, lag when crafting, ect) and i have heard if you turn on JVM arguments and increase how much ram you put into minecraft it reduces lag. so i did, i put in 2G when i have 6G of ram and when i try to play it says "Error Occurred during Initialization of VM. Could not reserve enough space for #amount of KB for object heap." I dont get how i have 6 ram and i cant even put 2 ram into the game. Is there a thing where i can reduce the ram usage so i can use at least 2 gb on minecraft? thanks..

Your problem isn't going to be solved by allocating more RAM; it is an extremely widespread misconception that allocating more RAM makes the game run faster, which is a gross misunderstanding of how computers work; it is the CPU and GPU that do the actual processing of data; RAM is only an issue when your whole computer doesn't have enough and swaps memory to disk. Otherwise, insufficient memory allocated to Minecraft will cause it to crash with an out of memory error. Even 512 MB is enough to run the game without problems, provided you aren't using extreme render distances (the game doesn't let you go over 16 chunks anyway unless you allocate more than 2 GB). The default JVM arguments in the launcher were also selected to help optimize java for Minecraft; you shouldn't have to change them.

See here for an analysis of memory usage, which comes to the conclusion that the problem with 32 bit Java has nothing to do with it being limited to 2 GB of total memory - this is very likely why you can't allocate 2 GB (1-1.5 GB is the max you can allocate); however, you should still install 64 bit Java (x64)not because you can allocate more memory but because 1.8 has serious performance issues when running on 32 bit for some reason; Java 8 (which I linked to) also appears to improve performance on 1.8.

Also, what are your system specs, particularly CPU and GPU (if on Windows, type "dxdiag" without quotes into the Run dialog box and you should see something like this; the GPU is under the "display" tab)? See here for the recommended system requirements; I also strongly believe that what they list as the recommended should actually be the minimum based on how many people with better systems report issues (i.e. the minimum should be what you need to run the game on minimum settings). Note also the bit version of your OS; if it says 32 bit then you cannot use 64 bit Java unless you upgrade your OS to 64 bit (which is a much more complicated task).

In addition, you didn't mention if you are using Optifine but it can help; in particular, you should turn off water particles. However, your issue appears to be mainly server lag (you didn't mention FPS issues), which can only be reduced by lowering render distance and the number of chunks loaded.

My specs are:

CPU: Intel Pentium Dual Core E5400 @ 2.70 Ghz

GPU: nvidia Geforce GT 520

RAM: 6

OS: Windows 7 64 bit

I am using optifine, and i dont really get bad fps(like when moving and other stuff) its just the stuff i said before, blocks appearing again after destroyed, ect. i use 1.8.1, and i just installed java 64 bit(i had java but dont know if i had the 64 bit). The only server that i had have terrible FPS is wynncraft but it mostly when i only ride a horse and sometimes just walking and fighting. I experience the lag i said before in singleplayer survival to, not just server survival. If you could help me further, please do

Does this only happen in one world, and if it does, do you have any big farms or redstone? I'd heard reports that 1.8 doesn't handle large numbers of entities (mobs) very well; e.g. a farm that runs fine in 1.7.10 causes lag in 1.8 which goes away when it is reduced.

Also, are there any warnings or errors in the game output (if necessary, click on edit profile in the launcher and ensure the launcher stays open), besides the "can't keep up messages" I suspect you are getting (which aren't really indicative of anything themselves). As mentioned above, if it only happens on one world there might be a problem with it (though it can usually be fixed).

(not related but when I tried Java 8 I started getting periods of lag when playing on 1.6.4, and when I looked in the logs I found a bunch of "item entity # has no item" errors from the client, which lead me to think there might be world corruption - it just turned out to be Java though; it didn't make any difference on 1.8 for me, where I also have lag, mostly FPS related, I can't install 64 bit since my OS is 32 bit)