pgsql: Fix some inconsistencies with GUC categories

Fix some inconsistencies with GUC categories This commit addresses a few things around GUCs: - The TCP-related parameters (the four tcp_keepalives_* and client_connection_check_interval are listed in postgresql.conf.sample in a subsection called "TCP settings" of "CONNECTIONS AND AUTHENTICATION",

pgsql: doc: mention that COPY MATCH requires columns _in_ _order_

doc: mention that COPY MATCH requires columns _in_ _order_ Question asked at SCaLE conference. Reported-by: doc suggestion by Stephen Frost Backpatch-through: 15 Branch -- master Details --- https://git.postgresql.org/pg/commitdiff/356dd2ce5b7b0f3ea11e016f73b1f173604b8452 Modified Fil

pgsql: doc: mention that COPY MATCH requires columns _in_ _order_

doc: mention that COPY MATCH requires columns _in_ _order_ Question asked at SCaLE conference. Reported-by: doc suggestion by Stephen Frost Backpatch-through: 15 Branch -- REL_15_STABLE Details --- https://git.postgresql.org/pg/commitdiff/b876b7e2d12786b101ad178fae29cd6a3d9137e9 Modif

pgsql: Introduce optimized routine for linear searches of arrays

Introduce optimized routine for linear searches of arrays Use SSE2 intrinsics to speed up the search, where available. Otherwise, use a simple 'for' loop. The motivation to add this now is to speed up XidInMVCCSnapshot(), which is the reason only unsigned 32-bit integer arrays are optimized. Oth