cursorFetchSize

How many rows the driver buffers per round-trip during streaming reads. Used by readCursor on every dialect, and additionally by the eager read path on Oracle, whose driver default would otherwise turn a bulk read into a round-trip storm.

On PostgreSQL and MySQL the value doubles as the streaming activation gate — 0 keeps the driver in eager full-buffer mode, positive values open a server-side cursor. On Oracle and the native drivers the value is purely a throughput knob: larger means fewer round-trips at the cost of a larger pre-allocated buffer.

The default 256 is a balanced choice: within roughly 10 % of arbitrarily large fetch sizes on every driver, and well clear of the memory-pressure point on wide schemas. Tune up (e.g. 1000) for narrow rows on high-latency links; tune down (e.g. 64) for VARCHAR2(4000)-heavy Oracle schemas where the pre-allocated buffer dominates memory. Override per call via readCursor's fetchSize parameter.