#!/usr/bin/env bash
# What pg_stat_progress_create_index shows in REINDEX CONCURRENTLY's wait
# for readers when the wait before it, for old snapshots, waited on two or
# more transactions (it may also count a session that was polling the view
# when it took its list).  WaitForOlderSnapshots() leaves lockers_done at
# that wait's count, and the wait for readers only sets lockers_total, so
# the view shows lockers_done greater than lockers_total.  Every step waits
# for the view to show the state it needs.  Any build; on a PROGRESS_DEBUG
# build the trace is on and its WAITFOR lines are printed too.
#   repro-waitfor.sh <bindir> <workdir>
set -euo pipefail
BIN=$1 W=$2; rm -rf "$W"; mkdir -p "$W"
export LD_LIBRARY_PATH=$BIN/../lib
PGDATA=$W/data; PORT=$((20000 + RANDOM % 10000))
export PGHOST=$W PGPORT=$PORT PGDATABASE=postgres
cleanup() {
  exec 3>&- 4>&- 5>&- 2>/dev/null || true
  "$BIN/pg_ctl" -D "$PGDATA" -m immediate -w stop >/dev/null 2>&1 || true
}
trap cleanup EXIT
"$BIN/initdb" -A trust -N -D "$PGDATA" >/dev/null
TR=; "$BIN/postgres" -D "$PGDATA" -C trace_progress >/dev/null 2>&1 && TR='-c trace_progress=on'
"$BIN/pg_ctl" -D "$PGDATA" -o "-p $PORT -k $W -c autovacuum=off $TR" -l "$W/log" -w start >/dev/null
q() { "$BIN/psql" -X -At -c "$1"; }
until_true() {
  for _ in $(seq 300); do [ "$(q "$1")" = t ] && return 0; sleep 0.1; done
  echo "timed out waiting for: $1" >&2; exit 1
}
q "CREATE TABLE t (a int); CREATE INDEX t_a ON t (a);
   INSERT INTO t SELECT generate_series(1, 1000); CREATE TABLE u (a int)" >/dev/null
for s in 1 2 3; do mkfifo "$W/s$s"; "$BIN/psql" -X -At <"$W/s$s" >"$W/s$s.out" 2>&1 & done
exec 3>"$W/s1" 4>"$W/s2" 5>"$W/s3"
# two old snapshots, no lock on t
for fd in 3 4; do
  echo "BEGIN ISOLATION LEVEL REPEATABLE READ; SELECT count(*) FROM u;" >&$fd
done
until_true "SELECT count(*) = 2 FROM pg_stat_activity
             WHERE state = 'idle in transaction' AND backend_xmin IS NOT NULL"
"$BIN/psql" -X -q -c 'REINDEX TABLE CONCURRENTLY t' & R=$!
until_true "SELECT coalesce(bool_or(phase = 'waiting for old snapshots'
             AND lockers_total >= 2), false) FROM pg_stat_progress_create_index"
echo "--- during the wait for old snapshots:"
q "SELECT 'lockers_total=' || lockers_total FROM pg_stat_progress_create_index"
# a reader of t, which the wait for readers will wait on
echo "BEGIN; SELECT count(*) FROM t;" >&5
until_true "SELECT count(*) = 1 FROM pg_locks l JOIN pg_stat_activity a USING (pid)
             WHERE l.relation = 't'::regclass AND a.state = 'idle in transaction'"
# end both old snapshots
echo "COMMIT;" >&3
echo "COMMIT;" >&4
until_true "SELECT coalesce(bool_or(phase = 'waiting for readers before marking dead'), false)
             FROM pg_stat_progress_create_index"
echo "--- during the wait for readers:"
q "SELECT 'phase=' || phase || ' lockers_total=' || lockers_total ||
          ' lockers_done=' || lockers_done
     FROM pg_stat_progress_create_index"
echo "COMMIT;" >&5
wait $R
exec 3>&- 4>&- 5>&-; wait
"$BIN/pg_ctl" -D "$PGDATA" -w stop >/dev/null
if [ -n "$TR" ]; then
  echo "--- trace: the WAITFOR parameters (3 total, 4 done, 5 pid) and phases (0):"
  grep -E 'LOG:  progress (start|end|update|incr|multi).*CREATE_INDEX' "$W/log" |
    sed -E 's/^.*LOG:  progress //' | grep -E '(^| )(0|3|4|5):|start|end' | sed 's/^/  /'
fi