My guess is that the transaction doing: update "planscheduleitem" set "planschedule"=$1 where "psi"=$2
updates ticket before reaching that point And update ticket set unread = true where ticketid = $1 updates planscheduleitem before that Does it make sense to you? Btw, do the transactions use explicit locking? 2018-02-18 23:28 GMT-06:00 David Wheeler <da...@inomial.com>: > Hi, > > We’re seeing deadlock semi-regularly (0-2 per day) that I’m really having > trouble getting to the bottom of. > > Process 7172 waits for ShareLock on transaction 4078724272 > <(407)%20872-4272>; blocked by process 7186. > Process 7186 waits for ShareLock on transaction 4078724210 > <(407)%20872-4210>; blocked by process 7172. > > The two queries in question are updates on unrelated tables. Running the > queries on their own shows no overlapping entries in pg_locks. > > Process 7172: update ticket set unread = true where ticketid = $1 > Process 7186: update "planscheduleitem" set "planschedule"=$1 where > "psi"=$2 > > How can I work out why Postgres has decided that the two processes are in > deadlock? Is there an explainer somewhere on transaction level locks? I > can’t see anything in the docs besides that they exist. > > > > Details below > > select version(); > version > ------------------------------------------------------------ > ----------------------------------------------------------------------- > PostgreSQL 10.2 (Ubuntu 10.2-1.pgdg14.04+1) on x86_64-pc-linux-gnu, > compiled by gcc (Ubuntu 4.8.4-2ubuntu1~14.04.3) 4.8.4, 64-bit > (1 row) > > ------------------------------------------------------------ > ------------------------------------------------------------ > ------------------------------- > > > after running update "planscheduleitem" set "planschedule"=$1 where > "psi"=$2 > > SELECT locktype, virtualxid, transactionid, virtualtransaction, pid, mode, > relname, page, tuple > FROM pg_locks LEFT JOIN pg_class ON (relation=oid) where pid =41715; > locktype | virtualxid | transactionid | virtualtransaction | pid | > mode | relname | page | tuple > ---------------+------------+---------------+--------------- > -----+-------+------------------+-------------------------+------+------- > relation | | | 56/2306863 | 41715 | > RowExclusiveLock | ticket_parentticketid | | > relation | | | 56/2306863 | 41715 | > RowExclusiveLock | ticket_originalticketid | | > relation | | | 56/2306863 | 41715 | > RowExclusiveLock | ticket_tickettypeid_idx | | > relation | | | 56/2306863 | 41715 | > RowExclusiveLock | ticket_subject_idx | | > relation | | | 56/2306863 | 41715 | > RowExclusiveLock | ticket_closedtime_idx | | > relation | | | 56/2306863 | 41715 | > RowExclusiveLock | ticket_assignedto_idx | | > relation | | | 56/2306863 | 41715 | > RowExclusiveLock | ticket_serviceuid_idx | | > relation | | | 56/2306863 | 41715 | > RowExclusiveLock | ticket_parentuid_idx | | > relation | | | 56/2306863 | 41715 | > RowExclusiveLock | ticket_createdtime_idx | | > relation | | | 56/2306863 | 41715 | > RowExclusiveLock | ticket_txid | | > relation | | | 56/2306863 | 41715 | > RowExclusiveLock | ticket_tickettype | | > relation | | | 56/2306863 | 41715 | > RowExclusiveLock | ticket_ticketpriority | | > relation | | | 56/2306863 | 41715 | > RowExclusiveLock | ticket_idx_0 | | > relation | | | 56/2306863 | 41715 | > RowExclusiveLock | ticket_pkey | | > relation | | | 56/2306863 | 41715 | > RowExclusiveLock | number_constraint | | > relation | | | 56/2306863 | 41715 | > RowExclusiveLock | ticket | | > virtualxid | 56/2306863 | | 56/2306863 | 41715 | > ExclusiveLock | | | > transactionid | | 4089785154 <(408)%20978-5154> | > 56/2306863 | 41715 | ExclusiveLock | | > | > relation | | | 56/2306863 | 41715 | > RowExclusiveLock | ticket_fromuid_idx | | > (19 rows) > > ------------------------------------------------------------ > ------------------------------------------------------------ > -------------------------------- > > after running update ticket set unread = true where ticketid = $1 > > SELECT locktype, virtualxid, transactionid, virtualtransaction, pid, mode, > relname, page, tuple > FROM pg_locks LEFT JOIN pg_class ON (relation=oid) where pid =41715; > locktype | virtualxid | transactionid | virtualtransaction | pid | > mode | relname | page | tuple > ---------------+------------+---------------+--------------- > -----+-------+------------------+--------------------------- > -----------+------+------- > relation | | | 56/2306861 | 41715 | > RowExclusiveLock | planscheduleitem_plan_company_idx | | > relation | | | 56/2306861 | 41715 | > RowExclusiveLock | psi_uid_startdate | | > relation | | | 56/2306861 | 41715 | > RowExclusiveLock | psi_planschedule_startdate_starttime | | > relation | | | 56/2306861 | 41715 | > RowExclusiveLock | planscheduleitem_pkey | | > relation | | | 56/2306861 | 41715 | > RowExclusiveLock | planscheduleitem | | > virtualxid | 56/2306861 | | 56/2306861 | 41715 | > ExclusiveLock | | | > transactionid | | 4089783283 <(408)%20978-3283> | > 56/2306861 | 41715 | ExclusiveLock | > | | > (7 rows) > > TIA > > Cheers, > > -- David > > > <http://www.inomial.com/> > > <http://www.inomial.com/>*David Wheeler* • software engineer > *Inomial Pty Ltd* • Automatic Billing <http://www.inomial.com/> > *p* +61 3 9663 3554 <+61%203%209663%203554> > > > <http://www.linkedin.com/company/inomial-pty-ltd> > <https://www.facebook.com/Inomial> <https://twitter.com/inomial> > <https://twitter.com/inomial> > -- El genio es 1% inspiración y 99% transpiración. Thomas Alva Edison http://pglearn.blogspot.mx/
