Relations statistics:
         relname          | pg_relpages 
--------------------------+-------------
 table: testcase1         |       25001
(1 row)

         relname          | pg_relpages 
--------------------------+-------------
 index: testcase1_multiid |         276
(1 row)

         relname          | pg_relpages 
--------------------------+-------------
 table: testcase2         |        2163
(1 row)

         relname          | pg_relpages 
--------------------------+-------------
 index: testcase2_multiid |        1099
(1 row)

Executing index query to cache index
Executing index query to collect statistics
Timing is on.
PERFORM  FROM testcase2 WHERE multi_id > i
 executeindexquery 
-------------------
 
(1 row)

Time: 95,034 ms
Statstics after call
                 relname                 | buffers 
-----------------------------------------+---------
 testcase2                               |    1072
 testcase2_multiid                       |     545
 testcase1_multiid                       |     138
 pg_class                                |       8
 pg_proc                                 |       7
 pg_proc_oid_index                       |       7
 pg_attribute_relid_attnum_index         |       6
 pg_attribute                            |       6
 pg_proc_proname_args_nsp_index          |       5
 pg_operator_oprname_l_r_n_index         |       4
 pg_statistic_relid_att_inh_index        |       4
 pg_class_relname_nsp_index              |       4
 pg_amop_fam_strat_index                 |       3
 pg_type                                 |       3
 pg_type_typname_nsp_index               |       3
 pg_statistic                            |       3
 pg_operator                             |       3
 pg_amop_opr_fam_index                   |       3
 pg_index                                |       3
 pg_operator_oid_index                   |       3
 pg_cast                                 |       2
 pg_class_oid_index                      |       2
 pg_index_indrelid_index                 |       2
 pg_amop                                 |       2
 pg_namespace_nspname_index              |       2
 pg_database_datname_index               |       2
 pg_tablespace_oid_index                 |       2
 pg_type_oid_index                       |       2
 pg_rewrite_rel_rulename_index           |       2
 pg_opclass_oid_index                    |       2
 pg_cast_source_target_index             |       2
 pg_aggregate_fnoid_index                |       2
 pg_opclass_am_name_nsp_index            |       2
 pg_language_oid_index                   |       2
 pg_amproc_fam_proc_index                |       2
 pg_index_indexrelid_index               |       2
 pg_opclass                              |       2
 pg_tablespace                           |       1
 pg_database_oid_index                   |       1
 pg_amproc                               |       1
 pg_language                             |       1
 pg_database                             |       1
 pg_aggregate                            |       1
 pg_authid_oid_index                     |       1
 pg_authid_rolname_index                 |       1
 pg_namespace                            |       1
 pg_authid                               |       1
 pg_rewrite                              |       1
 pg_db_role_setting_databaseid_rol_index |       1
(49 rows)

Time: 6,187 ms
Executing buffer overfull query
Timing is on.
Executing buffer overwrite by calling PERFORM substr(content, 1, 1) FROM testcase1 WHERE multi_id > 50000 + 10;
 executebufferoverwrite 
------------------------
 
(1 row)

Time: 463,381 ms
Statstics after call (top 20)
             relname              | buffers 
----------------------------------+---------
 testcase1                        |    1099
 testcase2_multiid                |     542
 testcase1_multiid                |     138
 pg_proc_oid_index                |       7
 pg_proc                          |       7
 pg_attribute                     |       5
 pg_proc_proname_args_nsp_index   |       4
 pg_attribute_relid_attnum_index  |       4
 pg_amop_opr_fam_index            |       3
 pg_operator_oid_index            |       3
 pg_statistic_relid_att_inh_index |       3
 pg_operator_oprname_l_r_n_index  |       3
 pg_type                          |       3
 pg_amop_fam_strat_index          |       3
 pg_class_relname_nsp_index       |       3
 pg_type_typname_nsp_index        |       3
 pg_tablespace_oid_index          |       2
 pg_class_oid_index               |       2
 pg_amop                          |       2
 pg_cast                          |       2
(20 rows)

Time: 6,382 ms
Trying to drop system caches to emphasise results...
(this may fail if you are not root user)
This is required to emphasise and show situation when reading overwrited
system buffers, too. Actually no drop buffers gives almost no difference
because memory copy of 545*8192 bytes is short.
3 > /proc/sys/vm/drop_caches ...
Executing index query to collect statistics, after full overfull
Timing is on.
PERFORM  FROM testcase2 WHERE multi_id > i
 executeindexquery 
-------------------
 
(1 row)

Time: 94,167 ms
Statstics after call
                 relname                 | buffers 
-----------------------------------------+---------
 testcase2                               |    1072
 testcase2_multiid                       |     545
 testcase1_multiid                       |     138
 pg_proc                                 |       7
 pg_attribute                            |       7
 pg_proc_oid_index                       |       7
 pg_attribute_relid_attnum_index         |       6
 pg_proc_proname_args_nsp_index          |       5
 pg_class                                |       4
 pg_statistic_relid_att_inh_index        |       4
 pg_operator_oprname_l_r_n_index         |       4
 pg_class_relname_nsp_index              |       4
 pg_statistic                            |       3
 pg_operator                             |       3
 pg_operator_oid_index                   |       3
 pg_amop_fam_strat_index                 |       3
 pg_amop_opr_fam_index                   |       3
 pg_index                                |       3
 pg_type                                 |       3
 pg_type_typname_nsp_index               |       3
 pg_opclass_am_name_nsp_index            |       2
 pg_class_oid_index                      |       2
 pg_index_indrelid_index                 |       2
 pg_authid_oid_index                     |       2
 pg_amop                                 |       2
 pg_namespace_nspname_index              |       2
 pg_database_datname_index               |       2
 pg_tablespace_oid_index                 |       2
 pg_type_oid_index                       |       2
 pg_rewrite_rel_rulename_index           |       2
 pg_opclass_oid_index                    |       2
 pg_cast_source_target_index             |       2
 pg_aggregate_fnoid_index                |       2
 pg_opclass                              |       2
 pg_language_oid_index                   |       2
 pg_amproc_fam_proc_index                |       2
 pg_database_oid_index                   |       2
 pg_index_indexrelid_index               |       2
 pg_cast                                 |       2
 pg_language                             |       1
 pg_namespace                            |       1
 pg_rewrite                              |       1
 pg_tablespace                           |       1
 pg_database                             |       1
 pg_aggregate                            |       1
 pg_authid_rolname_index                 |       1
 pg_db_role_setting_databaseid_rol_index |       1
 pg_authid                               |       1
 pg_am                                   |       1
 pg_amproc                               |       1
(50 rows)

Time: 6,198 ms
