rsdb/esm/buffersize_kb is a SAP Parameter attribute which is used to control Size of 'export to/import from shared memory'-(ESM)-buffer [kB] information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
This parameter defines the size of the ESM buffer in KB. The buffer is
used to store data in shared memory and is addressed by the ABAP
commands EXPORT TO / IMPORT FROM SHARED MEMORY and DELETE FROM SHARED
MEMORY. The commands only have an effect locally; the buffers of
external application servers are not changed. If the buffer is full, no
further objects can be stored in the buffer.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.