> DeĀ : Tom Lane [mailto:[EMAIL PROTECTED] > > "Daniel Caune" <[EMAIL PROTECTED]> writes: > > I did the following test, removing all the where-clause from the SELECT > statement. Every statement completes immediately, i.e. it doesn't block. > > I think you left out some critical information, like who else was doing > what to the table. > > What it looks like to me is that the third and fourth rows in this view > were live according to your transaction snapshot, but were committed > dead as of current time, and so FOR UPDATE wouldn't return them. > > > agoratokens=> select id from "Tokens" where id IN (47, 104, 44, 42) > limit 3 for update; > > This time, the statement returns the row where id equals to 44. > > No, it returns *some* row where id equals 44. Not necessarily the same > one seen in the seqscan. (I imagine this query is using an index, and > so would visit rows in a different physical order.) Printing the ctid > of the rows would confirm or disprove that theory. > > regards, tom lane
Thanks Tom. I think this time you will point me out the problem. The column id has a primary key constraint on. There should not be more than one row with id equals to 44. agoratokens=> \d "Tokens" Table "public.Tokens" Column | Type | Modifiers -----------+--------------------------------+------------------------------------------------------- id | integer | not null default nextval('"Tokens_id_seq"'::regclass) type | integer | not null value | character varying(255) | not null isLocked | boolean | not null default false timestamp | timestamp(6) without time zone | Indexes: "Tokens_pkey" PRIMARY KEY, btree (id) (...) agoratokens=> select ctid, * from "Tokens" where "isLocked" = true limit 3 for update; ctid | id | type | value | isLocked | timestamp ------+----+------+-------+----------+----------- (0 rows) agoratokens=> select ctid, * from "Tokens" where "isLocked" = true limit 3; ctid | id | type | value | isLocked | timestamp -----------+----+------+-------+----------+--------------------------- (199,84) | 44 | 3 | 3 | t | 2007-04-03 12:12:02.46944 (199,114) | 42 | 3 | 1 | t | 2007-04-03 13:00:44.877 (2 rows) agoratokens=> select ctid, * from "Tokens" where id = 44; ctid | id | type | value | isLocked | timestamp -----------+----+------+-------+----------+---------------------------- (3702,85) | 44 | 3 | 3 | f | 2007-11-22 16:41:33.494371 (1 row) agoratokens=> select count(*) from "Tokens" where id = 44; count ------- 1 (1 row) It seems that, in certain condition, row (199,84) is shadowing row (3702,85); my feeling from a "customer" high level. Indeed, as a PostgreSQL core developer, that assertion could make you laugh... :-) I took into account your point about the concurrent context. Therefore I isolated the database from any connection except mine. # TYPE DATABASE USER IP-ADDRESS IP-MASK METHOD local all all trust host all all 127.0.0.1 255.255.255.0 password #host all all 10.3.41.0 255.255.254.0 password sudo /etc/init.d/postgresql-8.1 restart * Restarting PostgreSQL 8.1 database server [ ok ] No other client than my psql was connected to PostgreSQL. You can trust me. The result is exactly the same: agoratokens=> select ctid, * from "Tokens" where "isLocked" = true limit 3; ctid | id | type | value | isLocked | timestamp -----------+----+------+-------+----------+--------------------------- (199,84) | 44 | 3 | 3 | t | 2007-04-03 12:12:02.46944 (199,114) | 42 | 3 | 1 | t | 2007-04-03 13:00:44.877 (2 rows) agoratokens=> select ctid, * from "Tokens" where id = 44; ctid | id | type | value | isLocked | timestamp -----------+----+------+-------+----------+---------------------------- (3702,85) | 44 | 3 | 3 | f | 2007-11-22 16:41:33.494371 (1 row) agoratokens=> select ctid, * from "Tokens" where "isLocked" = true limit 3; ctid | id | type | value | isLocked | timestamp -----------+----+------+-------+----------+--------------------------- (199,84) | 44 | 3 | 3 | t | 2007-04-03 12:12:02.46944 (199,114) | 42 | 3 | 1 | t | 2007-04-03 13:00:44.877 (2 rows) agoratokens=> select ctid, * from "Tokens" where id = 44; ctid | id | type | value | isLocked | timestamp -----------+----+------+-------+----------+---------------------------- (3702,85) | 44 | 3 | 3 | f | 2007-11-22 16:41:33.494371 (1 row) agoratokens=> select count(*) from "Tokens" where id = 44; count ------- 1 (1 row) By the way, according to the "business logic", the timestamp "2007-04-03 12:12:02.46944" is weird, because too old. I apologize if my question is stupid because of my knowledge lack, but would it possible that for some reasons the related SELECT statement uses an old snapshot? Regards, -- Daniel ---------------------------(end of broadcast)--------------------------- TIP 5: don't forget to increase your free space map settings