Why wouldn't VACUUM ANALYZE clear all dead tuples?

We run a "manual" VACUUM ANALYZE VERBOSE on some of our larger tables after we do major DELETE/INSERT changes to them. This seems to work without issue although sometimes a table's VACUUM job will run for hours (see this post for similar issues and reasoning). On doing more research I found that we have large tables with a large number of dead tuples even after running VACUUM. For example, here are some of the stats produced from the query in this response . -[ RECORD 50 ]--+--------------------------- relname | example_a last_vacuum | 2014-09-23 01:43 last_autovacuum | 2014-08-01 01:19 n_tup | 199,169,568 dead_tup | 111,048,906 av_threshold | 39,833,964 expect_av | * -[ RECORD 51 ]--+--------------------------- relname | example_b last_vacuum | 2014-09-23 01:48 last_autovacuum | 2014-08-30 12:40 n_tup | 216,596,624 dead_tup | 117,224,220 av_threshold | 43,319,375 expect_av | * -[ RECORD 52 ]--+--------------------------- relname | example_c last_vacuum | 2014-09-23 01:55 last_autovacuum | 2014-09-23 18:25 n_tup | 309,831,136 dead_tup | 125,047,233 av_threshold | 61,966,277 expect_av | * The last field states that these (and most tables) would meet the threshold for autovacuum. However, having just run VACUUM ANALYZE VEBOSE on each of those tables, shouldn't the dead tuple count be 0 (or close to 0, not 125M of 300M)? The documentation states: > VACUUM reclaims storage occupied by dead tuples. Does this mean our VACUUM is not working? ---------- **UPDATE** Per request in repsonse here are some logs from the VERBOSE jobs: INFO: vacuuming "public.example_1" INFO: scanned index "idx_example_1_on_gp_id_and_dd_id" to remove 378386 row versions DETAIL: CPU 1.83s/3.42u sec elapsed 23.01 sec. INFO: scanned index "index_example_1_on_q_id" to remove 378386 row versions DETAIL: CPU 2.10s/3.91u sec elapsed 18.92 sec. INFO: "example_1": removed 378386 row versions in 7085 pages DETAIL: CPU 0.09s/0.05u sec elapsed 0.19 sec. INFO: index "idx_example_1_on_gp_id_and_dd_id" now contains 30347438 row versions in 291065 pages DETAIL: 378386 index row versions were removed. 165587 index pages have been deleted, 164287 are currently reusable. CPU 0.00s/0.00u sec elapsed 0.00 sec. INFO: index "index_example_1_on_q_id" now contains 30347438 row versions in 333287 pages DETAIL: 378386 index row versions were removed. 152773 index pages have been deleted, 152757 are currently reusable. CPU 0.00s/0.00u sec elapsed 0.00 sec. INFO: "example_1": found 1773 removable, 401984 nonremovable row versions in 14438 out of 1493006 pages DETAIL: 0 dead row versions cannot be removed yet. There were 10567 unused item pointers. 0 pages are entirely empty. CPU 4.26s/7.51u sec elapsed 46.10 sec. INFO: vacuuming "pg_toast.pg_toast_17917" INFO: index "pg_toast_17917_index" now contains 0 row versions in 1 pages DETAIL: 0 index row versions were removed. 0 index pages have been deleted, 0 are currently reusable. CPU 0.00s/0.00u sec elapsed 0.00 sec. INFO: "pg_toast_17917": found 0 removable, 0 nonremovable row versions in 0 out of 0 pages DETAIL: 0 dead row versions cannot be removed yet. There were 0 unused item pointers. 0 pages are entirely empty. CPU 0.00s/0.00u sec elapsed 0.00 sec. INFO: analyzing "public.example_1" INFO: "example_1": scanned 30000 of 1493006 pages, containing 611502 live rows and 0 dead rows; 30000 rows in sample, 40563141 estimated total rows This table now shows 0 dead tuples in the stats. Most of the tables are much lower dead tuples this morning so either our VACUUM or autovacuum is working. We do have a handful of tables that output nothing and yet still show dead tuples: -[ RECORD 49 ]--+--------------------------- relname | example_2 last_vacuum | 2014-09-23 02:23 last_autovacuum | 2014-09-02 14:30 n_tup | 117,914,944 dead_tup | 34,507,388 av_threshold | 23,583,039 expect_av | * A couple times I have seen in the logs where the indexes will get checked over and over again. This seems to correspond to long-running VACUUM jobs. Any idea why? Is this just working around record locking (I don't think any writes were happening during this jobs run.) INFO: vacuuming "public.example_2" ... INFO: scanned index "index_example_2_on_gsg_id_and_dd_id" to remove 2795959 row versions DETAIL: CPU 3.88s/16.54u sec elapsed 23.09 sec. INFO: scanned index "index_example_2_on_q_id" to remove 2795959 row versions DETAIL: CPU 6.74s/21.13u sec elapsed 84.64 sec. INFO: "example_2": removed 2795959 row versions in 48214 pages DETAIL: CPU 0.71s/0.32u sec elapsed 33.65 sec. INFO: scanned index "index_example_2_on_gsg_id_and_dd_id" to remove 2591011 row versions DETAIL: CPU 2.84s/16.11u sec elapsed 19.28 sec. INFO: scanned index "index_example_2_on_q_id" to remove 2591011 row versions DETAIL: CPU 5.46s/22.70u sec elapsed 130.57 sec. INFO: "example_2": removed 2591011 row versions in 45539 pages DETAIL: CPU 0.67s/0.38u sec elapsed 15.16 sec. INFO: index "index_example_2_on_gsg_id_and_dd_id" now contains 123807784 row versions in 1560915 pages DETAIL: 108836958 index row versions were removed. 1100790 index pages have been deleted, 718471 are currently reusable. CPU 0.00s/0.00u sec elapsed 0.25 sec. INFO: index "index_example_2_on_q_id" now contains 123807784 row versions in 1886087 pages DETAIL: 110336259 index row versions were removed. 1058063 index pages have been deleted, 266983 are currently reusable. CPU 0.00s/0.00u sec elapsed 0.07 sec. INFO: "example_2": found 124808 removable, 1355901 nonremovable row versions in 2086343 out of 6966379 pages DETAIL: 0 dead row versions cannot be removed yet. There were 7858495 unused item pointers. 0 pages are entirely empty. CPU 595.49s/2130.13u sec elapsed 5656.34 sec. INFO: vacuuming "pg_toast.pg_toast_18079" INFO: index "pg_toast_18079_index" now contains 0 row versions in 1 pages DETAIL: 0 index row versions were removed. 0 index pages have been deleted, 0 are currently reusable. CPU 0.00s/0.00u sec elapsed 0.00 sec. INFO: "pg_toast_18079": found 0 removable, 0 nonremovable row versions in 0 out of 0 pages DETAIL: 0 dead row versions cannot be removed yet. There were 0 unused item pointers. 0 pages are entirely empty. CPU 0.00s/0.00u sec elapsed 0.00 sec. INFO: analyzing "public.example_2" INFO: "example_2": scanned 30000 of 6966379 pages, containing 528443 live rows and 522 dead rows; 30000 rows in sample, 152953760 estimated total rows