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Make native_agg_deletes stable on an assert build #162

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Merged
jdatcmd merged 1 commit into from
Jul 26, 2026
Merged

Make native_agg_deletes stable on an assert build #162

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31 changes: 23 additions & 8 deletions test/native_agg_deletes.sh
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Original file line number Diff line number Diff line change
Expand Up @@ -18,10 +18,10 @@
# once from the scan that covers it.
#
# 2. count(*) no longer cares. Timed as a ratio against the same query on the
# same table with nothing deleted, because a millisecond threshold is not
# portable. count(*) over a group is its row count minus its deleted count,
# which is exact, so a delete should cost it almost nothing. Before the change
# this ratio was in the thousands.
# same table scanned in full, because a millisecond threshold is not portable.
# count(*) over a group is its row count minus its deleted count, which is
# exact, so a delete should not send the query back to reading the table.
# Before the change it did exactly that.
#
# 3. Only the dirty groups are read. min/max cannot be folded from a zone map
# once a row is gone, so those groups are scanned -- but only those. Timed
Expand Down Expand Up @@ -116,11 +116,26 @@ clean_ms="$(ms "SELECT count(*) FROM ad_t")"
psql_run "DELETE FROM ad_t WHERE id = $((ROWS / 2));" >/dev/null 2>&1
dirty_ms="$(ms "SELECT count(*) FROM ad_t")"

echo "-- count(*): ${clean_ms} ms with no deletes, ${dirty_ms} ms with one"
# The reference is a full scan of the same table, not the undeleted timing.
#
# Comparing the deleted timing against the clean one looked like the obvious
# ratio and is the wrong shape: the clean figure is a metadata read of about
# 0.03 ms, so any jitter at all moves the ratio by tens. On an assert-enabled
# build -- which is what the matrix runs -- that failed about one run in three,
# at 1.1960/0.0320 against a threshold of 20, while the behaviour under test was
# perfectly correct.
#
# What the issue is actually about is that one deleted row must not send count(*)
# back to reading the table. So the thing to measure against is reading the
# table, which is milliseconds rather than microseconds and does not swing.
scan_ms="$(ms "SELECT count(*) FROM ad_t" \
"SET pgcolumnar.enable_vectorization = off;")"

echo "-- count(*): ${clean_ms} ms clean, ${dirty_ms} ms with one deleted, ${scan_ms} ms scanning"

check "one deleted row does not put count(*) into a different class" \
"$(awk -v c="$clean_ms" -v d="$dirty_ms" \
'BEGIN { print (c > 0 && d / c < 20) ? "yes" : "no (" d "/" c ")" }')" \
check "one deleted row does not send count(*) back to a full scan" \
"$(awk -v d="$dirty_ms" -v s="$scan_ms" \
'BEGIN { print (s > 0 && d < s / 4) ? "yes" : "no (" d " against a " s " scan)" }')" \
"yes"

# --- 3. only the groups with deletes are read ----------------------------------
Expand Down