[pgsql-ru-general] deadlock при drop index concurrently

Вот что видим в логах:

Mar 23 15:45:07 mdb postgres[26481]: [177-1] user=pgsql,db=geo,client=10.77.255.13 ERROR:  deadlock detected

Mar 23 15:45:07 mdb postgres[26481]: [177-2] user=pgsql,db=geo,client=10.77.255.13 DETAIL:  Process 26481 waits for ShareLock on virtual transaction 8/29343079; blocked by process 15087.

Mar 23 15:45:07 mdb postgres[26481]: [177-3]        Process 15087 waits for AccessExclusiveLock on relation 24694 of database 17701; blocked by process 26481.

Mar 23 15:45:07 mdb postgres[26481]: [177-4]        Process 26481: DROP INDEX CONCURRENTLY IF EXISTS geo_11_2gis_get_route_platform_ids_from_json

Mar 23 15:45:07 mdb postgres[26481]: [177-5]        

Mar 23 15:45:07 mdb postgres[26481]: [177-6]        Process 15087: LOCK TABLE geo_11 IN ACCESS EXCLUSIVE MODE

Mar 23 15:45:07 mdb postgres[26481]: [177-7] user=pgsql,db=geo,client=10.77.255.13 HINT:  See server log for query details.

Mar 23 15:45:07 mdb postgres[26481]: [177-8] user=pgsql,db=geo,client=10.77.255.13 STATEMENT:  DROP INDEX CONCURRENTLY IF EXISTS geo_11_2gis_get_route_platform_ids_from_json

Mar 23 15:45:07 mdb postgres[26481]: [177-9]

кто-нибудь может объяснить откуда мог взяться при указании конкурентности дедлок?

версия postgres 9.4.4