# Architecture

> Architecture, catalogs, replication, execution, I/O, roles, and server internals.

---

LLMS index: [llms.txt](/en/llms.txt)

---

<div class="feature-source-note"><span class="feature-edition-badge">GA</span><span><strong>Source pages:</strong> PDF 13-31</span><span><a href="https://github.com/nori-shinoda/documents/blob/1773200c5362476c4a549222b7d17fa91f546cae/postgresql12_ga_new_features_en_20191011-1.pdf">Original PDF on GitHub</a></span></div>

<p class="feature-page-marker" id="pgfeat-12-architecture-pdf-page-13">PDF page 13</p>

#### 3.1.1 Modified catalogs {#pg12-3-1-1-modified-catalogs}

The following catalogs have been changed.

**Table 4.** Added system catalogs

| Catalog name | Description |
| --- | --- |
| pg_stat_progress_cluster | Traces the execution status of CLUSTER. |
| pg_stat_progress_create_index | Traces the execution status of CREATE INEDX. |
| pg_stat_gssapi | Showing information about GSSAPI usage. |
| pg_statistic_ext_data | Holds data for extended planner statistic |

**Table 5.** Added information\_schema catalog

| Catalog name | Description |
| --- | --- |
| column_column_usage | Column information that depends on a specific column (stores information on a table with generated columns). |

**Table 6.** System catalogs with columns added

| Catalog name | Added column | Data type | Description |
| --- | --- | --- | --- |
| *1 | oid | oid | Change attribute to regular column. |
| pg_attribute | attgenerated | char | 's' for generated column. |
| pg_collation | collisdeterministic | boolean | Is the collation deterministic? |
| pg_statistic | stacol[1-5] | oid | Collation information. |
| pg_stat_database | checksum_failures | bigint | Number of blocks for which a checksum error was detected. |
|  | checksum_last_failure | timestamp with time zone | Last timestamp for which checksum error was detected. |
| pg_stat_replication | reply_time | timestamp with time zone | Message time from standby instance. |
| pg_stat_ssl | client_serial | numeric | Client certificate serial number. |
|  | issuer_dn | text | Client certificate issuer DN. |

<p class="feature-page-marker" id="pgfeat-12-architecture-pdf-page-14">PDF page 14</p>

*1 There are many corresponding catalogs.

**Table 7.** System catalogs with columns deleted

| Catalog name | Deleted column | Description |
| --- | --- | --- |
| pg_attrdef | adsrc | A human-readable representation of the default value. |
| pg_class | relhasoids | Whether the table is WITH OIDS specified. |
| pg_constraint | consrc | A human-readable representation of the expression. |
| pg_statistic_ext | stxndistinct | Move to pg_statistics_ext_data |
|  | stxdependencies | Move to pg_statistics_ext_data |

**Table 8.** System catalogs with column modified

| Catalog name | Modified Column | Description |
| --- | --- | --- |
| pg_shadow | valuntil | Data type changed to timestamp with time zone. |
| pg_stat_ssl | client_dn | Column name changed from 'lientdn'. |

Among the modified system catalogs, the details of the major catalogs are described below.

##### Pg_stat_progress_cluster catalog {#pg12-p14-pg-stat-progress-cluster-catalog}

The pg_stat_progress_cluster catalog can trace the execution status of CLUSTER statements or VACUUM FULL statements.

**Table 9.** pg\_stat\_progress\_cluster catalog

| Column name | Data type | Description |
| --- | --- | --- |
| pid | integer | Process ID of backend. |
| datid | oid | OID of the database to which this backend is connected. |
| datname | name | Name of the database to which this backend is connected. |
| relid | oid | OID of the table being clustered. |
| command | text | The command that is running. |
| phase | text | Current processing phase. |
| cluster_index_relid | oid | OID of the index being used. |
| heap_tuples_scanned | bigint | Number of heap tuples scanned. |
| heap_tuples_written | bigint | Number of heap tuples written. |
| heap_blks_total | bigint | Total number of heap blocks in the table. |
| heap_blks_scanned | bigint | Number of heap blocks scanned. |
| index_rebuild_count | bigint | Number of indexes rebuilt. |

<p class="feature-page-marker" id="pgfeat-12-architecture-pdf-page-15">PDF page 15</p>

##### Pg_stat_progress_create_index catalog {#pg12-p15-pg-stat-progress-create-index-catalog}

The pg_stat_progress_create_index catalog can trace the execution status of CREATE INDEX statement. The status is also reflected when the REINDEX statement is executed.

**Table 10.** pg\_stat\_progress\_create\_index catalog

| Column name | Data type | Description |
| --- | --- | --- |
| pid | integer | Process ID of backend. |
| datid | oid | OID of the database to which this backend is connected. |
| datname | name | Name of the database to which this backend is connected. |
| relid | oid | OID of the table on which the index is being created. |
| index_relid | oid | OID of the index. |
| command | text | Executed SQL statement name. |
| phase | text | Current processing phase of index creation. |
| lockers_total | bigint | Total number of lockers to wait for. |
| lockers_done | bigint | Total number of lockers already waited for. |
| current_locker_pid | bigint | Process ID of the locker currently being waited for. |
| blocks_total | bigint | Total number of the blocks to be processed. |
| blocks_done | bigint | Total number of the blocks already processed. |
| tuples_total | bigint | Total number of tuples to be processed. |
| tuples_done | bigint | Number of tuples already processed. |
| partitions_total | bigint | Total number of partitions. |
| partitions_done | bigint | Number of partitions on which the index has been completed. |

<p class="feature-page-marker" id="pgfeat-12-architecture-pdf-page-16">PDF page 16</p>

**Example 8.** Refer pg\_stat\_progress\_create\_index catalog

```text
postgres=> SELECT * FROM pg_stat_progress_create_index ;
-[ RECORD 1 ]------+---------------------------------------
pid                | 13233
datid              | 16385
datname            | postgres
relid              | 16386
index_relid       | 0
phase              | building index: loading tuples in tree
lockers_total      | 0
lockers_done       | 0
current_locker_pid | 0
blocks_total       | 0
blocks_done        | 0
tuples_total       | 10000000
tuples_done        | 6207353
partitions_total   | 0
partitions_done    | 0
```

##### Pg_stat_replication catalog {#pg12-p16-pg-stat-replication-catalog}

The reply_time column has been added to the pg_stat_replication catalog. This column stores the sending time of the last reply message received from the standby instance. This column can only be displayed by the SUPERUSER attribute or the holder of the pg_monitor role.

<p class="feature-page-marker" id="pgfeat-12-architecture-pdf-page-17">PDF page 17</p>

**Example 9.** Refer pg\_stat\_replication catalog

```text
postgres=# SELECT * FROM pg_stat_replication ;
-[ RECORD 1 ]----+------------------------------
pid              | 12497
usesysid         | 10
usename          | postgres
application_name | walreceiver
client_addr      |
client_hostname  |
client_port      | -1
backend_start    | 2019-10-03 20:13:15.551032-04
backend_xmin     |
state            | streaming
sent_lsn         | 0/3000060
write_lsn        | 0/3000060
flush_lsn        | 0/3000060
replay_lsn       | 0/3000060
write_lag        |
flush_lag        |
replay_lag       |
sync_priority    | 0
sync_state       | async
reply_time       | 2019-10-03 20:15:45.68363-04
```

##### Pg_indexes catalog {#pg12-p17-pg-indexes-catalog}

The pg_indexes catalog now includes partitioned indexes. Specifically, the relkind column in the pg_class catalog now includes an index of 'I'.

##### Pg_stat_database catalog {#pg12-p17-pg-stat-database-catalog}

The checksum_failures column and checksum_last_failure column in the pg_stat_database catalog are now updated when a block checksum error is detected. The value of checksum_failures column is updated each time when a checksum error is detected, so it does not indicate the actual number of blocks corrupted.

<p class="feature-page-marker" id="pgfeat-12-architecture-pdf-page-18">PDF page 18</p>

**Example 10.** Refer pg\_stat\_database catalog

```text
postgres=# SELECT * FROM data1 ;
psql: WARNING:  page verification failed, calculated checksum 27311
but expected 12320
ERROR:  invalid page in block 0 of relation base/13567/16384
postgres=#
postgres=# SELECT datname, checksum_failures , checksum_last_failure
FROM pg_stat_database WHERE datname='postgres' ;
-[ RECORD 1 ]-----+------------------------------
datname           | postgres
checksum_failures | 1
checksum_last_failure | 2019-10-03 20:06:23.747741-04
```

```text
In PostgreSQL 12, a tuple whose datid column is 0 has been added. This is database-independent
global object information.
```

##### Pg_stat_gssapi catalog {#pg12-p18-pg-stat-gssapi-catalog}

The pg_stat_gssapi view showing information about GSSAPI usage on this connection. It can be joined to pg_stat_activity or pg_stat_replication on the pid column to get more details about the connection.

**Table 11.** pg\_stat\_gssapi catalog

| Column name | Data type | Description |
| --- | --- | --- |
| pid | integer | Process ID of backend. |
| gss_authenticated | boolean | True if GSSAPI authentication was used. |
| principal | text | Principal used to authenticate this connection. |
| encrypted | boolean | True if GSSAPI encryption is in use. |

##### Pg_statistic_ext_data catalog {#pg12-p18-pg-statistic-ext-data-catalog}

This catalog holds data for extended planner statistics defined in pg_statistic_ext.

<p class="feature-page-marker" id="pgfeat-12-architecture-pdf-page-19">PDF page 19</p>

**Table 12.** pg\_statistic\_ext\_data catalog

| Column name | Data type | Description |
| --- | --- | --- |
| stxoid | oid | Reference of pg_statistic_ext catalog |
| stxdndistinct | pg_ndistinct | N-distinct counts |
| stxddependencies | pg_dependencies | Functional dependency statistics |
| stxdmcv | pg_mcv_list | MCV (most-common values) list statistics |

#### 3.1.2 Abolition of recovery.conf file {#pg12-3-1-2-abolition-of-recovery-conf-file}

The recovery.conf file used to build standby instances in a streaming replication environment, and for recovery from backup has been obsolete. Various settings in the recovery.conf file have been integrated into the postgresql.conf file. Some parameters have been changed.

**Table 13.** Modified parameters

| recovery.conf | postgresql.conf | Note |
| --- | --- | --- |
| standby_modetrigger_file | promote_trigger_file | Discontinued. |

In case of recovery, create a recovery.signal file in the database cluster and start the instance. This file is deleted when the recovery process is complete. In a streaming replication environment, create a standby.signal file in the database cluster on slave instances. This file is deleted when promoted to primary. If the recovery.conf file exists in the database cluster, instance startup fails.

<p class="feature-page-marker" id="pgfeat-12-architecture-pdf-page-20">PDF page 20</p>

**Example 11.** Deploy recovery\.conf file and start instance

```bash
$ ls data/recovery.conf
data/recovery.conf
$ pg_ctl -D data start
waiting for server to start....2019-10-03 21:55:53.749 EDT [18397]
LOG:  starting PostgreSQL 12.0 on x86_64-pc-linux-gnu, compiled by
gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-36), 64-bit
2019-10-03 21:55:53.750 EDT [18397] LOG:  listening on IPv6 address
"::1", port 5432
2019-10-03 21:55:53.750 EDT [18397] LOG:  listening on IPv4 address
"127.0.0.1", port 5432
2019-10-03 21:55:53.755 EDT [18397] LOG:  listening on Unix socket
"/tmp/.s.PGSQL.5432"
2019-10-03 21:55:53.771 EDT [18398] LOG:  database system was shut
down at 2019-10-03 21:55:09 EDT
2019-10-03 21:55:53.771 EDT [18398] FATAL:  using recovery command
file "recovery.conf" is not supported
2019-10-03 21:55:53.772 EDT [18397] LOG:  startup process (PID
18398) exited with exit code 1
2019-10-03 21:55:53.772 EDT [18397] LOG:  aborting startup due to
startup process failure
2019-10-03 21:55:53.773 EDT [18397] LOG:  database system is shut
down
 stopped waiting
pg_ctl: could not start server
Examine the log output.
$
```

#### 3.1.3 Instance startup log {#pg12-3-1-3-instance-startup-log}

The version number is now output to the log at instance startup. If the parameter logging_collector is specified as "on", it is output to the log file.

<p class="feature-page-marker" id="pgfeat-12-architecture-pdf-page-21">PDF page 21</p>

**Example 12.** Instance startup log

```bash
$ pg_ctl -D data start
waiting for server to start....2019-10-03 21:36:22.445 EDT [17730]
LOG:  starting PostgreSQL 12.0 on x86_64-pc-linux-gnu, compiled by
gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-36), 64-bit
2019-10-03 21:36:22.447 EDT [17730] LOG:  listening on IPv6 address
"::1", port 5432
2019-10-03 21:36:22.447 EDT [17730] LOG:  listening on IPv4 address
"127.0.0.1", …
```

#### 3.1.4 Maximum number of connections {#pg12-3-1-4-maximum-number-of-connections}

The number of connections for replication is now obtained using the max_wal_senders parameter without depending on the max_connections parameter. As a result of this modification, information of max_wal_senders has been added to the output of the pg_controldata command.

**Example 13.** Output of pg\_controldata command

```bash
$ pg_controldata -D data | grep max_wal_senders
max_wal_senders setting:              10
```

#### 3.1.5 Parallel query enhancement {#pg12-3-1-5-parallel-query-enhancement}

Parallel queries now work even if the transaction isolation level of the session is SERIALIZABLE. The following example uses the auto_explain module to output the execution plan of the SQL statement executed in the transaction of the SERIALIZABLE isolation level.

<p class="feature-page-marker" id="pgfeat-12-architecture-pdf-page-22">PDF page 22</p>

**Example 14.** Execute query

```text
postgres=# LOAD 'auto_explain' ;
LOAD
postgres=# SET auto_explain.log_min_duration = 0 ;
SET
postgres=# BEGIN ISOLATION LEVEL SERIALIZABLE ;
BEGIN
postgres=# SELECT COUNT(*) FROM data1 ;
  count
---------
 1000000
(1 row)
postgres=# COMMIT ;
COMMIT
```

**Example 15.** Execution plan on PostgreSQL 11

```sql
2019-10-03 21:52:48.785 JST [1789] LOG:  duration: 45.472 ms  plan:
        Query Text: SELECT COUNT(*) FROM data1 ;
        Aggregate  (cost=17906.00..17906.01 rows=1 width=8)
          ->  Seq Scan on data1  (cost=0.00..15406.00 rows=1000000
width=0)
```

**Example 16.** Execution plan of PostgreSQL 12

```sql
2019-10-03 21:39:09.319 EDT [17764] LOG:  duration: 94.678 ms  plan:
        Query Text: SELECT COUNT(*) FROM data1;
        Finalize Aggregate  (cost=10633.55..10633.56 rows=1 width=8)
          ->  Gather  (cost=10633.33..10633.54 rows=2 width=8)
                Workers Planned: 2
                ->  Partial Aggregate  (cost=9633.33..9633.34 rows=1
width=8)
                      ->  Parallel Seq Scan on data1  (cost=0.00..8591.67
rows=416667 width=0)
```

<p class="feature-page-marker" id="pgfeat-12-architecture-pdf-page-23">PDF page 23</p>

#### 3.1.6 Jsonb type and GIN index {#pg12-3-1-6-jsonb-type-and-gin-index}

The "jsonb @@ jsonpath" and "jsonb @? jsonpath" operators have been added to the GIN index created for the jsonb type. The operator class of GIN index can be used either jsonb_ops or json_path_ops. The following is the execution plan of the SELECT statement described in the manual.

**Example 17.** jsonb type and GIN index

```text
postgres=> CREATE INDEX idxgin ON api USING GIN (jdoc) ;
CREATE INDEX
postgres=> EXPLAIN (COSTS OFF) SELECT jdoc->'guid', jdoc->'name' FROM
api WHERE jdoc @@ '$.tags[*] == "qui"' ;
                            QUERY PLAN
------------------------------------------------------------------
 Bitmap Heap Scan on api
   Recheck Cond: (jdoc @@ '($."tags"[*] == "qui")'::jsonpath)
   ->  Bitmap Index Scan on idxgin
         Index Cond: (jdoc @@ '($."tags"[*] == "qui")'::jsonpath)
(4 rows)
postgres=> EXPLAIN (COSTS OFF) SELECT jdoc->'guid', jdoc->'name' FROM
api WHERE jdoc @@ '$.tags[*] ? (@ == "qui")' ;
                             QUERY PLAN
--------------------------------------------------------------------
 Bitmap Heap Scan on api
   Recheck Cond: (jdoc @@ '$."tags"[*]?(@ == "qui")'::jsonpath)
   ->  Bitmap Index Scan on idxgin
         Index Cond: (jdoc @@ '$."tags"[*]?(@ == "qui")'::jsonpath)
(4 rows)
```

#### 3.1.7 Wait Event {#pg12-3-1-7-wait-event}

The following changes were made to the wait event output to the wait_event column of the pg_stat_activity catalog.

<p class="feature-page-marker" id="pgfeat-12-architecture-pdf-page-24">PDF page 24</p>

**Table 14.** Modified wait events

| Wait event name | Description | Modify |
| --- | --- | --- |
| BackendRandomLock | Waiting to generate a random number. | Deleted |
| GSSOpenServer | Waiting for connect to GSSAPI server. | Added |
| CheckpointDone | Waiting for a checkpoint to complete. | Added |
| CheckpointStart | Waiting for a checkpoint to start. | Added |
| Promote | Waiting for standby promotion. | Added |
| WALSync | Waiting for a WAL file to reach stable storage. | Added |

#### 3.1.8 ECPG {#pg12-3-1-8-ecpg}

The following features have been added to ECPG.

##### Bytea data type {#pg12-p24-bytea-data-type}

The variable of type bytea is defined in the DECLARE SECTION and can be used for data input/output.

**Example 18.** DECLARE bytea

```sql
{
    EXEC SQL BEGIN DECLARE SECTION ;
        bytea data[1024] ;
        short data_ind = 0 ;
    EXEC SQL END DECLARE SECTION ;
    memset(data.arr, 0, sizeof(data.arr)) ;
    data.len = 0 ;
    EXEC SQL SELECT col1 INTO :data FROM data1 ;
    for (i = 0; i < data.len; i++)
    {
        printf("data[%d] = %c\n", i, data.arr[i]) ;
    }
}
```

<p class="feature-page-marker" id="pgfeat-12-architecture-pdf-page-25">PDF page 25</p>

##### PREPARE AS statement {#pg12-p25-prepare-as-statement}

It is now possible to write SQL statements directly by PREPARE AS statement.

**Example 19.** PREPARE AS statement

```sql
{
    EXEC SQL BEGIN DECLARE SECTION ;
        int ivar1 = 100;
    int ivar2 = 200;
    EXEC SQL END DECLARE SECTION ;
  EXEC SQL PREPARE pre_name(INT, INT) AS INSERT INTO prepare1
VALUES ($1, $2);
    EXEC SQL EXECUTE pre_name(:ivar1, :ivar2);
}
```

#### 3.1.9 Pluggable Storage Engine {#pg12-3-1-9-pluggable-storage-engine}

The basic specifications for using multiple storage engines have been decided. The access method for the table specifies the TYPE TABLE clause in the CREATE ACCESS METHOD statement. Syntax

```sql
CREATE ACCESS METHOD am_name TYPE TABLE HANDLER handler_name
```

The default storage engine is specified by the default_table_access_method parameter. The default value for this parameter is "heap". As a result of this modification, it has been added tuple to the pg_am catalog.

<p class="feature-page-marker" id="pgfeat-12-architecture-pdf-page-26">PDF page 26</p>

**Example 20.** Refer pg\_am catalog

```text
postgres=# SELECT amname, amhandler, amtype FROM pg_am ;
 amname |      amhandler       | amtype
--------+----------------------+--------
 heap   | heap_tableam_handler | t
 btree  | bthandler            | i
 hash   | hashhandler          | i
 gist   | gisthandler          | i
 gin    | ginhandler           | i
 spgist | spghandler           | i
 brin   | brinhandler          | i
(7 rows)
```

##### Specify engine when creating table {#pg12-p26-specify-engine-when-creating-table}

To specify a storage engine for a table, specify the USING clause in the CREATE TABLE statement. It can also be specified with the CREATE TABLE AS SELECT statement or the CREATE MATERIALIZED VIEW statement.

**Example 21.** CREATE TABLE statement

```text
postgres=> CREATE TABLE data1(c1 NUMERIC, c2 VARCHAR(10)) USING
heap ;
CREATE TABLE
postgres=> CREATE TABLE data2 USING heap AS SELECT * FROM data1 ;
SELECT 100000
postgres=> CREATE MATERIALIZED VIEW mview1 USING heap AS
                 SELECT COUNT(*) cnt FROM data1 ;
SELECT 1
```

##### Display table definition by psql command {#pg12-p26-display-table-definition-by-psql-command}

When the "\d+ table_name" command is executed, the storage engine name of the table is output.

<p class="feature-page-marker" id="pgfeat-12-architecture-pdf-page-27">PDF page 27</p>

**Example 22.** \\d\+ command output

```text
postgres=> \d+ data1
                                          Table "public.data1"
 Column |         Type          | Collation | Nullable | Default | Storage  | Stats
target | Description
--------+-----------------------+-----------+----------+---------+----------+---
-----------+-
 c1     | numeric               |           |          |         | main     |           |
 c2     | character varying(10) |           |          |         | extended |
|
Access method: heap
```

```text
 Specifying on for the psql variable HIDE_TABLEAM (default value: 'off') can suppress the output
of the Access Method item.
```

**Example 23.** \\d\+ command output

```text
postgres=> \set HIDE_TABLEAM on
postgres=> \d+ data1
                                          Table "public.data1"
 Column |         Type          | Collation | Nullable | Default | Storage  | Stats
target | Description
--------+-----------------------+-----------+----------+---------+----------+--------
------+----------
 c1     | numeric               |           |          |         | main     |           |
 c2     | character varying(10) |           |          |         | extended |           |
```

##### Display of access method by psql command {#pg12-p27-display-of-access-method-by-psql-command}

Table access methods are also displayed with the \dA command. Previously, only the index access method was output.

<p class="feature-page-marker" id="pgfeat-12-architecture-pdf-page-28">PDF page 28</p>

**Example 24.** \\dA command output

```text
postgres=> \dA
List of access methods
  Name  | Type
--------+-------
 brin   | Index
 btree  | Index
 gin    | Index
 gist   | Index
 hash   | Index
 heap   | Table
 spgist | Index
(7 rows)
```

#### 3.1.10 Pg_hba.conf file {#pg12-3-1-10-pg-hba-conf-file}

The following new features have been added to the pg_hba.conf file.

##### New parameter of clientcert item {#pg12-p28-new-parameter-of-clientcert-item}

A new setting "verfy-full" can be specified for the clientcert parameter. This option also ensures that the certificate's "cn" (common name) matches the username or proper mapping.

##### GSSAPI authentication encryption option {#pg12-p28-gssapi-authentication-encryption-option}

Generic Security Standard Application Programming Interface (GSSAPI) with encryption option is available for client authentication. An entry of hostgssenc / hostnogssenc can be specified in the pg_hba.conf file. In order to enable GSSAPI authentication, it is necessary to specify --with-gssapi as an option of "configure" command at installation.

#### 3.1.11 Text search {#pg12-3-1-11-text-search}

Supported languages for text search increased. It was 16 languages in PostgreSQL 11 but has increased to 22 languages in PostgreSQL 12.

<p class="feature-page-marker" id="pgfeat-12-architecture-pdf-page-29">PDF page 29</p>

**Example 25.** Text search configurations

```text
postgres=# \dF
               List of text search configurations
   Schema   |    Name    |              Description
------------+------------+---------------------------------------
 pg_catalog | arabic     | configuration for arabic language
<< new
 pg_catalog | danish     | configuration for danish language
 pg_catalog | dutch      | configuration for dutch language
 pg_catalog | english    | configuration for english language
 pg_catalog | finnish    | configuration for finnish language
 pg_catalog | french     | configuration for french language
 pg_catalog | german     | configuration for german language
 pg_catalog | hungarian  | configuration for hungarian language
 pg_catalog | indonesian | configuration for indonesian language << new
 pg_catalog | irish      | configuration for irish language      << new
 pg_catalog | italian    | configuration for italian language
 pg_catalog | lithuanian | configuration for lithuanian language << new
 pg_catalog | nepali     | configuration for nepali language
 pg_catalog | norwegian  | configuration for norwegian language  << new
 pg_catalog | portuguese | configuration for portuguese language
 pg_catalog | romanian   | configuration for romanian language
 pg_catalog | russian    | configuration for russian language
 pg_catalog | simple     | simple configuration
 pg_catalog | spanish    | configuration for spanish language
 pg_catalog | swedish    | configuration for swedish language
 pg_catalog | tamil      | configuration for tamil language     << new
 pg_catalog | turkish    | configuration for turkish language
(22 rows)
```

<p class="feature-page-marker" id="pgfeat-12-architecture-pdf-page-30">PDF page 30</p>

#### 3.1.12 Libpq API {#pg12-3-1-12-libpq-api}

The following functions have been added to the C language interface to PostgreSQL.

##### PQresultMemorySize {#pg12-p30-pqresultmemorysize}

"size_t PQresultMemorySize (const PGresult * res)" API has been added. This function returns the amount of memory allocated by PGresult. It can be used to manage application memory.

##### GetForeignDataWrapperExtended {#pg12-p30-getforeigndatawrapperextended}

"ForeignDataWrapper * GetForeignDataWrapperExtended (Oid fwdid, bits16 flags)" API has been added.

##### GetForeignServerExtended {#pg12-p30-getforeignserverextended}

"ForeignServer * GetForeignServerExtended (Oid fwdid, bits16 flags)" API has been added.

#### 3.1.13 Transaction ID {#pg12-3-1-13-transaction-id}

The 64-bit transaction ID is available. API "GetTopFullTransactionId", "GetTopFullTransactionIdIfAny", "GetCurrentFullTransactionId" and "GetCurrentFullTransactionIdIfAny" are provided. However, the current heap does not use them.

#### 3.1.14 Client environment variable {#pg12-3-1-14-client-environment-variable}

Environment variables PG_COLOR and PG_COLORS have been added. Specify whether to use the color of the diagnostic message in PG_COLOR. Possible values are always, auto or never. PG_COLORS is specified by combining the category of escape sequence and code with an equal sign (=). When specifying multiple categories, separate them with a colon (:).

**Table 15.** Environment variable PG\_COLORS settings

| Category | Default value | Note |
| --- | --- | --- |
| error | 01;31 |  |
| warning | 01;35 |  |
| locus | 01 |  |

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#### 3.1.15 Client connection string {#pg12-3-1-15-client-connection-string}

Tcp_user_timeout indicating TCP timeout has been added to the client connection string.