I been having some problems with the PS3 lately. For instance, I was re playing Dark Souls and when I was in Undead Burg the assets didn't load correctly so it kinda was impossible to play. Since it was all grey, I could see the enemies and could walk, just couln't see where. After I started to notice that installing games and loading games was taking longer, I install bioshock infinite and took almost 3 hours. I don't remember that game did took that much the first time I install it. So, my question is. What exactly does "Rebuild Database"? Is kinda like defragmentation? could it help me? Also, does this delete save games/games/dlc's or anything like that?
It's not exactly a defrag, but it may solve the types of issues you're having nonetheless. From the PS3 Developer Wiki (and probably one of the older, no-longer-existent official support pages, given that this exact same text shows up in multiple places through a Google search):
This will rewrite corrupted files within the database, potentially eliminating future issues. This feature should not erase any of your saved data or settings (except some PSN account information). Deletes messages, playlists, changes made on "Information" screens, trimming information for pictures in "Photo", video thumbnails, video playback history and video resume information.
The process can take a pretty long time, and will likely sign you out of PSN, so make sure to log back in after it's done.