http://forums.musicbrainz.org/viewtopic.php?id=4625
http://forums.musicbrainz.org/viewtopic.php?id=4629

both report an issue with http://musicbrainz.org/release-group/9b4c2532-1006-40e0-bbe1-76e5f8dd9b30

The error message seems to be

Failed query:
'INSERT INTO "musicbrainz"."release_group" ("artist_credit", "comment", "edits_pending", "gid", "id", "last_updated", "name", "type") VALUES (?, ?, ?, ?, ?, ?, ?, ?)'
(602380 0 9b4c2532-1006-40e0-bbe1-76e5f8dd9b30 1320815 2013-11-23 01:17:49.599961+00 Lorem ipsum dolor sit amet,
.....LOADS OF TEXT HERE.....
)
DBD::Pg::st execute failed: ERROR: index row size 6608 exceeds maximum 2712 for index "release_group_idx_musicbrainz_collate"
HINT: Values larger than 1/3 of a buffer page cannot be indexed.
Consider a function index of an MD5 hash of the value, or use full text indexing. at /home/solace/repos/musicbrainz-server/admin/replication/../../lib/Sql.pm line 107.

at /home/solace/repos/musicbrainz-server/admin/replication/../../lib/Sql.pm line 113.
Sql::catch

Unknown macro: {...}

("DBD::Pg::st execute failed: ERROR: index row size 6608 excee"...) called at /home/solace/perl5/lib/perl5/Try/Tiny.pm line 106
Try::Tiny::try(CODE(0x231cf08), Try::Tiny::Catch=REF(0x231d688)) called at /home/solace/repos/musicbrainz-server/admin/replication/../../lib/Sql.pm line 114
Sql::do(Sql=HASH(0x219c418), "INSERT INTO \"musicbrainz\".\"release_group\" (\"artist_credit\", \""..., 602380, "", 0, "9b4c2532-1006-40e0-bbe1-76e5f8dd9b30", 1320815, "2013-11-23 01:17:49.599961+00", "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Done"..., ...) called at /home/solace/repos/musicbrainz-server/admin/replication/ProcessReplicationChanges line 284
main::mirrorInsert(Sql=HASH(0x21a88f8), Sql=HASH(0x219c418), ARRAY(0x2116838), 788205867) called at /home/solace/repos/musicbrainz-server/admin/replication/ProcessReplicationChanges line 252
main::mirrorCommand("i", Sql=HASH(0x21a88f8), Sql=HASH(0x219c418), ARRAY(0x2116838), 788205867, CODE(0x231cce0)) called at /home/solace/repos/musicbrainz-server/admin/replication/ProcessReplicationChanges line 181

Luks mentioned this on IRC as well:

2207 luks| it probably breaks all db slaves with the collate indexes
2207 luks| (fortunatelly, I don't have them in my dbs)