The database's round trip, and the check that a database-bound run is on its host

A grade, a comparison and the visit walks are bound by the database, so CLAUDE.md runs them on the database's own host. knw_db_latency() measures the connection: the median wall time of n SELECT 1 queries through DBI::dbGetQuery(), with no warm-up, which is the path the host's 1.6 ms and a remote link's 104 to 110 ms were measured on (2026-10-24, 2026-10-26). knw_db_latency_check() measures it and, over limit_ms, stops with the round trip and what a remote link cost #92's comparison, unless remote is TRUE. 0310, 0320 and 0330 call it at connect, before any work, and set remote from REMOTE=TRUE; each logs the returned line.

Usage

knw_db_latency(conn, n = 20)

knw_db_latency_check(conn, remote = FALSE, limit_ms = 20, n = 20)

Arguments

conn: a DBI connection.
n: integer(1) how many queries to time.
remote: logical(1): run over the limit anyway, and say so in line.
limit_ms: numeric(1) the round trip, in ms, above which the connection is taken to be off the host.

Value

knw_db_latency(): the median round trip in ms. knw_db_latency_check(): a list of ms, limit_ms, remote, over (the round trip is above the limit) and line, the measurement as one line for a log.

Details

What the remote link cost #92's 0330 (every key; the host on 2026-10-26, the remote link on 2026-10-27, so the ratios are approximate):

part of `0330`	host	remote link
classify, overlay and connect	115 min	164 min
the rest of the comparison	48 min	105 min
GeoPackages	14 min	197 min

Examples

if (FALSE) { # \dontrun{
conn <- DBI::dbConnect(RPostgres::Postgres())
knw_db_latency(conn)
knw_db_latency_check(conn)$line
} # }