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This patch generalizes libpq's existing single-row mode to allow individual partial-result PGresults to contain up to N rows, rather than always one row. This reduces malloc overhead compared to plain single-row mode, and it is very useful for psql's FETCH_COUNT feature, since otherwise we'd have to add code (and cycles) to either merge single-row PGresults into a bigger one or teach psql's results-printing logic to accept arrays of PGresults. To avoid API breakage, PQsetSingleRowMode() remains the same, and we add a new function PQsetChunkedRowsMode() to invoke the more general case. Also, PGresults obtained the old way continue to carry the PGRES_SINGLE_TUPLE status code, while if PQsetChunkedRowsMode() is used then their status code is PGRES_TUPLES_CHUNK. The underlying logic is the same either way, though. Daniel Vérité, reviewed by Laurenz Albe and myself (and whacked around a bit by me, so any remaining bugs are my fault) Discussion: https://postgr.es/m/CAKZiRmxsVTkO928CM+-ADvsMyePmU3L9DQCa9NwqjvLPcEe5QA@mail.gmail.com