Memory Management Functions

pg_shared_chunk_detail(contextname char(64))

Description: Queries information about all chunks requested by the memory context in a specified shared memory.

The contextname parameter indicates the name of the memory context.

Before using this function, use the pg_shared_chunk_dump(contextname char(64)) function to print related information to a file.

Return type: record

Example:

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SELECT * FROM pg_shared_chunk_detail('pgstat file hash table');
       parent        | level |  file_name   | line_number | chunk_size | requested_number | total_size 
---------------------+-------+--------------+-------------+------------+------------------+------------
 pgstat file context |     2 | dynahash.cpp |         158 |       2048 |                1 |       2048
 pgstat file context |     2 | dynahash.cpp |         158 |        256 |                1 |        256
 pgstat file context |     2 | dynahash.cpp |         158 |       4096 |                9 |      36864
 pgstat file context |     2 | dynahash.cpp |         158 |       8192 |                4 |      32768
(4 rows)

pv_session_chunk_detail(tid int, contextname char(64))

Description: Queries information about all chunks applied for by a memory context created by a specified thread.

The tid parameter indicates the thread ID, while the contextname parameter indicates the memory context name.

To use this function, you need to use the pv_session_chunk_dump(tid int, contextname char(64)) function to print related information to a file.

Return type: record

Example:

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SELECT * FROM pv_session_chunk_detail(140178810990936, 'Timezones');
      parent      | level |   file_name   | line_number | chunk_size | requested_number | total_size 
------------------+-------+---------------+-------------+------------+------------------+------------
 TopMemoryContext |     1 | dynahash.cpp  |         158 |       1280 |                2 |       2560
 TopMemoryContext |     1 | dynahash.cpp  |         158 |        160 |                1 |        160
 TopMemoryContext |     1 | dynahash.cpp  |         158 |       2560 |                2 |       5120
 TopMemoryContext |     1 | localtime.cpp |        1965 |        128 |                1 |        128
 TopMemoryContext |     1 | localtime.cpp |        1965 |        448 |                1 |        448
(5 rows)

pg_shared_chunk_dump(contextname char(64))

Description: Prints information about all chunks applied for by the memory context in the specified shared memory as a file.

The contextname parameter indicates the name of the memory context.

Return type: Boolean

Example:

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SELECT * FROM pg_shared_chunk_dump('pgstat file hash table');
 pg_shared_chunk_dump 
----------------------
         t
(1 row)

pv_session_chunk_dump(tid int, contextname char(64))

Description: Prints information about all chunks applied for by a memory context created by a specified thread into a file.

The tid parameter indicates the thread ID, while the contextname parameter indicates the memory context name.

Return type: Boolean

Example:

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SELECT * FROM pv_session_chunk_dump(140472797325280, 'Timezones');
 pv_session_chunk_dump 
-----------------------
 t
(1 row)

gs_print_memory_profiling()

Description: Prints memory collection details. This function is available only for clusters of version 9.1.1.100 or later.

Return type: Boolean

Example:

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SELECT * FROM gs_print_memory_profiling();
 gs_print_memory_profiling 
----------------------------
 t
(1 row)

gs_gsc_dbstat_info(database_id bigint DEFAULT NULL::bigint)

Description: Queries the statistics of Global SysCache on the current node, such as the SysCache cache hit information and LRU-based eviction. This function is available only for clusters of version 9.1.1.100 or later.

The parameter database_id indicate the database OID.

• When database_id is left blank, statistics about all databases are queried.
• When database_id is 0, the statistics of the shared database are queried.
• When database_id is a valid database OID, the statistics of the shared database and the database are queried.

Return type: record

Return columns:

Example:

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SELECT * FROM gs_gsc_dbstat_info();
 database_id | database_name | tup_searches | tup_hits | tup_miss | tup_swapout_count | tup_count | tup_dead | tup_memory | total_memory | refcount
-------------+---------------+--------------+----------+----------+-------------------+-----------+----------+------------+--------------+----------
           0 |               |        12474 |     9876 |       14 |                 0 |        16 |        0 |      12560 |       697664 |        0
       17185 | postgres      |        10156 |     5521 |     2223 |                 0 |      1398 |        0 |     752296 |      4417856 |       11
(2 rows)

gs_gsc_clean(database_id bigint DEFAULT NULL::bigint)

Description: Clears the Global SysCache of a specified database. This function is available only for clusters of version 9.1.1.100 or later.

The parameter database_id indicate the database OID.

• When database_id is left blank, the memory of all databases is cleared.
• When database_id is 0, the memory of the shared databases is cleared.
• When database_id is a valid database OID, the memory of both the shared databases and the specified database is cleared.

Return type: bool

Example:

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SELECT * FROM gs_gsc_clean();
 gs_gsc_clean
--------------
 t
(1 row)

gs_table_oscache(regclass)

Description: Queries the cache status of table data files in the OS file cache. This function is supported only by clusters of version 9.1.1.200 or later.

This function involves mmap locks and is not recommended to be used frequently.

Return type: record

The following table describes return columns.

Example:

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SELECT * FROM gs_table_oscache('employee');
 schema_name | table_name |    file_name     | file_type | seg_count | file_size | cache_size | con_cache_count | cache_dirty_size | con_cache_dirty_count | in_fd_cache
-------------+------------+------------------+-----------+-----------+-----------+------------+-----------------+------------------+-----------------------+-------------
 public      | employee   | base/17253/17103 | RowRel    |         1 |         0 |          0 |               0 |                0 |                     0 | f
(1 row)

gs_table_freecache(regclass)

Description: Clears the OS file cache of the data files of a specified table. This function cannot clear the data files that are still open. This function is supported only by clusters of version 9.1.1.200 or later.

Return type: bool

Example:

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SELECT * FROM gs_table_freecache('employee');
 gs_table_freecache
--------------------
 t
(1 row)

gs_file_freecache(IN file_path TEXT)

Description: Clears the OS file cache of a specified file. This function can clear files that are still open. This function is supported only by clusters of version 9.1.1.200 or later.

file_path: indicates the file path.

Return type: bool

Example:

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SELECT * FROM gs_file_freecache('base/17253/17103');
 gs_file_freecache
-------------------
 t
(1 row)