The batch_size configuration parameter determines the number of rows per batch the Full-Text Search engine indexes. batch_size has a default of 500 (that is, 500 rows of data indexed per batch). Performance improves if you increase the size of the batches that are indexed. However, the larger the batch size, the more memory the Full-Text Search engine allocates for this parameter.
When considering how large to set batch_size, consider the size of the data on which you are creating a text index. When creating the text index, the Full-Text Search engine allocates memory equal to (in bytes):
(amount of space needed for data) x (batch_size) = memory used
For example, if the data you are indexing is 10,000 bytes per row, and batch_size is set to 500, then the Full-Text Search engine will need to allocate almost 5MB of memory when creating the text index.
Base the batch size you choose on the typical size of your data and the amount of memory available on your machine.