Once the index has been created, there are many ways in which you can improve query resolution time. First of all, an index can be read from disk, memory-mapped, or directly loaded into main memory. These three solutions work with increasing speed and increased main memory usage. The default for quasi-succinct indices is to map the index in memory. Otherwise, the default is to read the index from disk. You can add suitable options to the index URI (e.g., mapped=1 or inmemory=1―see the Index.UriKeys documentation) to force your preferences. Analogously, offsets are necessary to locate, inside the index file, the posting list of a certain term. By default they are read from disk using a SemiExternalOffsetList, but you can load them in memory if you prefer so using the offsetstep parameter. If you load sizes (e.g., because you want to run a scorer that needs them) there is a suitable URI option (e.g., succinctsizes=1) that will load sizes in a highly compact format. This is particularly useful when pasting large indices.

To get more options, you can partition your index (see below). Once you have a cluster formed by several sub-indices, you can decide which sub-indices go to memory, which will be mapped, and so on.