Permalink
Switch branches/tags
Nothing to show
Find file
Fetching contributors…
Cannot retrieve contributors at this time
134 lines (128 sloc) 5.12 KB
create or replace function pgq.batch_event_sql(x_batch_id bigint)
returns text as $$
-- ----------------------------------------------------------------------
-- Function: pgq.batch_event_sql(1)
-- Creates SELECT statement that fetches events for this batch.
--
-- Parameters:
-- x_batch_id - ID of a active batch.
--
-- Returns:
-- SQL statement.
-- ----------------------------------------------------------------------
-- ----------------------------------------------------------------------
-- Algorithm description:
-- Given 2 snapshots, sn1 and sn2 with sn1 having xmin1, xmax1
-- and sn2 having xmin2, xmax2 create expression that filters
-- right txid's from event table.
--
-- Simplest solution would be
-- > WHERE ev_txid >= xmin1 AND ev_txid <= xmax2
-- > AND NOT txid_visible_in_snapshot(ev_txid, sn1)
-- > AND txid_visible_in_snapshot(ev_txid, sn2)
--
-- The simple solution has a problem with long transactions (xmin1 very low).
-- All the batches that happen when the long tx is active will need
-- to scan all events in that range. Here is 2 optimizations used:
--
-- 1) Use [xmax1..xmax2] for range scan. That limits the range to
-- txids that actually happened between two snapshots. For txids
-- in the range [xmin1..xmax1] look which ones were actually
-- committed between snapshots and search for them using exact
-- values using IN (..) list.
--
-- 2) As most TX are short, there could be lot of them that were
-- just below xmax1, but were committed before xmax2. So look
-- if there are ID's near xmax1 and lower the range to include
-- them, thus decresing size of IN (..) list.
-- ----------------------------------------------------------------------
declare
rec record;
sql text;
tbl text;
arr text;
part text;
select_fields text;
retry_expr text;
batch record;
begin
select s.sub_last_tick, s.sub_next_tick, s.sub_id, s.sub_queue,
txid_snapshot_xmax(last.tick_snapshot) as tx_start,
txid_snapshot_xmax(cur.tick_snapshot) as tx_end,
last.tick_snapshot as last_snapshot,
cur.tick_snapshot as cur_snapshot
into batch
from pgq.subscription s, pgq.tick last, pgq.tick cur
where s.sub_batch = x_batch_id
and last.tick_queue = s.sub_queue
and last.tick_id = s.sub_last_tick
and cur.tick_queue = s.sub_queue
and cur.tick_id = s.sub_next_tick;
if not found then
raise exception 'batch not found';
end if;
-- load older transactions
arr := '';
for rec in
-- active tx-es in prev_snapshot that were committed in cur_snapshot
select id1 from
txid_snapshot_xip(batch.last_snapshot) id1 left join
txid_snapshot_xip(batch.cur_snapshot) id2 on (id1 = id2)
where id2 is null
order by 1 desc
loop
-- try to avoid big IN expression, so try to include nearby
-- tx'es into range
if batch.tx_start - 100 <= rec.id1 then
batch.tx_start := rec.id1;
else
if arr = '' then
arr := rec.id1;
else
arr := arr || ',' || rec.id1;
end if;
end if;
end loop;
-- must match pgq.event_template
select_fields := 'select ev_id, ev_time, ev_txid, ev_retry, ev_type,'
|| ' ev_data, ev_extra1, ev_extra2, ev_extra3, ev_extra4';
retry_expr := ' and (ev_owner is null or ev_owner = '
|| batch.sub_id || ')';
-- now generate query that goes over all potential tables
sql := '';
for rec in
select xtbl from pgq.batch_event_tables(x_batch_id) xtbl
loop
tbl := rec.xtbl;
-- this gets newer queries that definitely are not in prev_snapshot
part := select_fields
|| ' from pgq.tick cur, pgq.tick last, ' || tbl || ' ev '
|| ' where cur.tick_id = ' || batch.sub_next_tick
|| ' and cur.tick_queue = ' || batch.sub_queue
|| ' and last.tick_id = ' || batch.sub_last_tick
|| ' and last.tick_queue = ' || batch.sub_queue
|| ' and ev.ev_txid >= ' || batch.tx_start
|| ' and ev.ev_txid <= ' || batch.tx_end
|| ' and txid_visible_in_snapshot(ev.ev_txid, cur.tick_snapshot)'
|| ' and not txid_visible_in_snapshot(ev.ev_txid, last.tick_snapshot)'
|| retry_expr;
-- now include older tx-es, that were ongoing
-- at the time of prev_snapshot
if arr <> '' then
part := part || ' union all '
|| select_fields || ' from ' || tbl || ' ev '
|| ' where ev.ev_txid in (' || arr || ')'
|| retry_expr;
end if;
if sql = '' then
sql := part;
else
sql := sql || ' union all ' || part;
end if;
end loop;
if sql = '' then
raise exception 'could not construct sql for batch %', x_batch_id;
end if;
return sql || ' order by 1';
end;
$$ language plpgsql; -- no perms needed