Treat all databases as time varying
Treat all databases as time varying is an option accessible from Main window -> Options -> Preferences. It is not described in User's Manual , but it can affect the performance significantly. It causes repopulation of database metadata every state change by calling PopulateDatabaseMetaData. For the case of big data files metadata population can take quite a lot of time and processing time raises enormously with number of time states increased.
Some simulations may decompose their mesh into many smaller domains or AMR patches. Over time, the simulation may change how the domains are decomposed, creating or deleting domains (this changes the SIL). Some simulations even add variables later in time that do not exist at early time. The Treat all databases as time varying option exists so the metadata will be retrieved anew each time the user visits a new time step of the simulation data so VisIt will be made aware of a domain decomposition that varies over time or variables that are added later. So, while being a potentially expensive operation, the Treat all databases as time varying option lets VisIt accurately visualize databases whose metadata changes over time.
VisIt's database metadata lets file format readers implicitly behave in the time-varying manner (e.g. the SAMRAI reader). Some file formats, however, which are not usually used to store data whose metadata varies over time are sometimes used in that manner (e.g. Silo). In that case, the Treat all databases as time varying option lets VisIt read the metadata for each time step just in case subsequent time steps require new metadata.
If you are using a database where the domain decomposition does not change and the list of variables is known in time step zero, then you do not need to use the Treat all databases as time varying option.