Deleted thumbnail file but no space was freed I'm using an xperia z3 and used file commander to browse and found that i kept running out of space because of a 4gb thumbnail/preview file/folder that grows rather quickly. I tried deleting the folder but after deleting the folder I saw that no space was freed and it was still there. So I tried moving the folder to my SD csrd which resulted in 4gb of space taken up on my SD card and no space freed. I dont think I can find the thumbnail previee folder anymore but I think new files are building up because I'm running oit of space again. Does anyone know whats going on?.
.thumbnails folder has a file of the format .thumbdata4* whose size is shown to be really big usually. But in reality, it's not a big file and it's size is shown as such is because it's not a normal file. It's a sparse file and it's real size can be seen using du command from a terminal emulator. ls shows the file size from it's metadata like most tools do and it'll be a big no.
On my phone, it looks like this
/storage/emulated/0/DCIM/.thumbnails $ du -h .thumbdata4--1967290299    
172K    .thumbdata4--1967290299 

/storage/emulated/0/DCIM/.thumbnails $ ls -alh .thumbdata4--1967290299                                                                  
-rw-rw---- 1 root sdcard_rw 11G 2020-07-30 19:18 .thumbdata4--1967290299

So it's actually a small file and you don't have to worry about it's size.
See the size difference. ls shows size to be 11GB while du shows it to be only 172KB.