Segment-Page Storage Functions
- To create a segment-page table on the Astore storage engine, you need to set segment to on when creating the table. For example:
CREATE TABLE t1(id int) WITH (segment=on, storage_type=astore);
- The values of the fields related to the segment-page storage function are described as follows:
- forknum: data file fork.
Value range: [0: mainfork; 1: fsmfork; 2: vm fork].
- file id: data file ID.
Value range: [1: metadata file; 2–5: data file].
- blocks: extent size.
Value range: [1: No.1 file; 8: No.2 file; 128: No.3 file; 1024: No.4 file; 4096: No.5 file].
- file_block_id/head_block_id/block_id: offset page number of the physical page in the data file and other fields that indicate the page number.
Value range: [0,4294967294]
- page_ type: page type.
Value range:
Meta pages: file head/file_header: file header; spc head/spc_header: space header; map head/map_header: mapping header; map page/map_pages: mapping page; reverse pointer page/inverse pointer page/ip pages: reverse pointer page; segment head page/segment head: segment header page; level1 page: level-1 page; data_pages/data extent: data page; fork head: fork header.
Data pages: heap, uheap, btree, and ubtree.
Unknown pages: unknown(data extent): all-zero segment page whose type cannot be determined; unknown(fsm indexurq): fsm or indexurq page.
- contents: storage content of a data file.
Value range: permanent (permanent), unlogged (no log), temporary (global temporary), and temporary2 (local temporary)
- forknum: data file fork.
- local_space_shrink(tablespacename TEXT, databasename TEXT)
Description: Shrinks specified physical segment-page space on the current node. Only the currently connected database can be shrank.
Return value: empty
- gs_space_shrink(tablespace int4, database int4, extent_type int4, forknum int4)
Description: Works similar to local_space_shrink, that is, shrinks specified physical segment-page space. However, the parameters are different. The input parameters are the OIDs of the tablespace and database, and the value of extent_type is an integer ranging from 2 to 5. Note: The value 1 of extent_type indicates segment-page metadata. Currently, the physical file that contains the metadata cannot be shrunk. This function is used only by tools. You are advised not to use it directly.
Return value: empty
- gs_stat_remain_segment_info()
Description: Runs on the primary node to query extents on the local node with residual data due to faults. By default, only initial users, users with the sysadmin permission, and users with the O&M administrator permission in the O&M mode can view the information. Other users can view the information only after being granted with permissions. This function can be executed only on the primary node. Residual extents are classified into two types: segments that are allocated but not used and extents that are allocated but not used. The main difference is that a segment contains multiple extents. During reclamation, all extents in the segment need to be recycled.
Return type
Name
Description
node_name
Node name.
space_id
Tablespace ID
db_id
Database ID
block_id
Extent ID
type
Extent type. The options are as follows: ALLOC_SEGMENT, DROP_SEGMENT, and SHRINK_EXTENT.
The values of type are described as follows:
- ALLOC_SEGMENT: When a user creates a segment-page table and the segment is just allocated but the transaction of creating a table is not committed, the node is faulty. As a result, the segment is not used after being allocated.
- DROP_SEGMENT: When a user deletes a segment-page table and the transaction is successfully committed, the bit corresponding to the segment page of the table is not reset and a fault, such as power failure, occurs. As a result, the segment is not used or released.
- SHRINK_EXTENT: When a user shrinks a segment-page table and does not release the idle extent, a fault, such as power failure, occurs. As a result, the extent remains and cannot be reused.
Example:
gaussdb=# SELECT * FROM gs_stat_remain_segment_info(); node_name | space_id | db_id | block_id | type ----------------+----------+-------+----------+--------------- dn_6001 | 16804 | 16803 | 4157 | ALLOC_SEGMENT (1 row)
- gs_free_remain_segment()
Description: Runs on the primary node to free segments queried by using the gs_stat_remain_segment_info function in the current database. By default, only initial users, users with the sysadmin permission, and users with the O&M administrator permission in the O&M mode can execute the function. Other users can use the function only after being granted with permissions. This function can be executed only on the primary node.
Return type: Boolean
- gs_local_stat_remain_segment_info()
Description: Runs on the primary node to query the residual segment page information of the current node. For details about user permissions and return values, see gs_stat_remain_segment_info.
- gs_local_free_remain_segment()
Description: Runs on the primary node to clear the residual segment page information of the current database on the current node. For details about user permissions and return values, see gs_free_remain_segment.
gs_seg_dump_page(tablespace_name name, file_id int4, bucketnode int4, file_block_id bigint, forknum int4 default 0)
Description: Parses a specified page in segment-page mode and returns the parsed content. Only users with the sysadmin attribute and users with the O&M administrator attribute in O&M mode can execute this function. This function is used to parse physical pages. The parsing result of one page is returned each time. The returned result does not contain the actual user data. This function does not require users to enter the page type. During implementation, the system attempts to determine the page type. If the page type cannot be determined, the system outputs possible parsing results.
Parameter description
Name
Type
Description
table_space_name
NAME
Tablespace to which a segment belongs. Value range: a valid tablespace name.
file_id
INTEGER
Data file ID. Value range: an int4 value in the range [1,5].
bucketnode
INTEGER
- 0 to 1023 indicate the bucket nodes of a hash bucket table.
- 1024 indicates the bucket node of a segment-page ordinary table.
- 1025 indicates the bucket node of a segment-page global temporary table.
- 1026 indicates the bucket node of a segment-page unlogged table.
- 1027 indicates the bucket node of a segment-page local temporary table.
file_block_id
BIGINT
Offset page number of the physical page in the data file. Value range: [0,4294967294]
forknum
INTEGER DEFAULT 0
Fork number of a data file. The default value is 0.
Value range:- 0: main fork.
- 1: FSM fork.
- 2: VM fork.
Return typeName
Type
Description
page_type
TEXT
Page type. Value range:
- Service pages: heap, uheap, btree, ubtree, gsivfflat_index, and gsdiskann_index
- Segment-page metapages: bucket main head, file head, spc head, map head, map page, reverse pointer page, segment head page and level1 page.
- Unknown pages:
- unknown(data extent): all-zero segment page whose type cannot be determined.
- unknown(fsm indexurq): fsm or indexurq page.
result
TEXT
Parsing result.
For example, perform the following operations after creating a segment-paged ordinary table:gaussdb=# SELECT * FROM gs_seg_dump_page('pg_default', 1, 1024, 4157); page_type | result -------------------+----------------------------------------------------------------------------- segment head page | Page information of block 4157/4157 + | pd_lsn: 0/2C90608 ,len 8 ,offset 0 + | + | pd_checksum: 0x8A7F, verify success,len 2, offset 8 + | pd_flags: + | pd_lower: 24, empty, len 2, offset 12 + | pd_upper: 8192, old, len 2, offset 14 + | pd_special: 8192, size 0, len 2, offset 16 + | Page size & version: 8192, 8, len 2, offset 18 + | pd_xid_base: 0, len 8, offset 24 pd_multi_base: 0, len 8, offset 32+ | pd_prune_xid: 0, len 4 ,offset 20 + | + | Segment head information on this page + | magic: 44414548544E454D + | lsn is: 0/2C90540 + | nblocks: 0 + | total_blocks: 8 + | reserved: 0 + | Level 0 slots information on this page + | The BlockNumber of level0 slots 0 is: 4157 + | fork head information on this page + | 4157(valid) + | 4294967295(invalid) + | 4294967295(invalid) (1 row)gs_seg_dump_page(relid oid, bucketnode int, block_id bigint, partition bool default false, forknum int4 default 0)
Description: Parses a specified page in segment-page mode and returns the parsed content. This function is executed on DNs. Only users with the sysadmin attribute and users with the O&M administrator attribute in O&M mode can execute this function. This function is used to parse logical pages. The parsing result of one page is returned each time. The returned result does not contain the actual user data. This function does not require users to enter the page type. During implementation, the system attempts to determine the page type. If the page type cannot be determined, the system outputs possible parsing results.
Parameter description
Name
Type
Description
relid
OID
Segment object ID. Value range: a valid segment-page object ID. Otherwise, an error is reported.
bucketnode
INTEGER
- 0 to 1023 indicate the bucket nodes of a hash bucket table.
- 1024 indicates the bucket node of a segment-page ordinary table.
- 1025 indicates the bucket node of a segment-page global temporary table.
- 1026 indicates the bucket node of a segment-page unlogged table.
- 1027 indicates the bucket node of a segment-page local temporary table.
block_id
BIGINT
Logical page number. Value range: [0,4294967294]
partition
BOOLEAN DEFAULT FALSE
Specifies whether the segment object is a partition. The default value is false. Value range: bool, indicating whether the object corresponding to the input OID is a partition.
forknum
INTEGER DEFAULT 0
Fork number of a data file. The default value is 0.
Value range:- 0: main fork.
- 1: FSM fork.
- 2: VM fork.
Return value descriptionName
Type
Description
page_type
TEXT
Page type. Value range:
- Service pages: heap, uheap, btree, ubtree, gsivfflat_index, and gsdiskann_index
- Segment-page metapages: bucket main head, file head, spc head, map head, map page, reverse pointer page, segment head page and level1 page.
- Unknown pages:
- unknown(data extent): all-zero segment page whose type cannot be determined.
- unknown(fsm indexurq): fsm or indexurq page.
result
TEXT
Parsing result.
In the following example, relid must be a valid OID of a multipart page object, and the object must have data so that the page information can be queried:gaussdb=# SELECT * FROM gs_seg_dump_page(16788, 1024, 0); page_type | result -----------+------------------------------------------------------------------------------------------------------------------------- heap | Page information of block 6021/6021 + | pd_lsn: 0/4463418 ,len 8 ,offset 0 + | + | pd_checksum: 0xD4CD, verify success,len 2, offset 8 + | pd_flags: + | pd_lower: 44, non-empty, len 2, offset 12 + | pd_upper: 8160, old, len 2, offset 14 + | pd_special: 8192, size 0, len 2, offset 16 + | Page size & version: 8192, 6, len 2, offset 18 + | pd_xid_base: 17049, len 8, offset 24 pd_multi_base: 0, len 8, offset 32 + | pd_prune_xid: 17049, len 4 ,offset 20 + | + | Heap tuple information on this page + | + | Tuple #1 is normal: length 28, offset 8160 + | (uint64)xmin/xmax/t_cid: 17052/0/0 + | (uint32)t_xmin/t_xmax: 3/3(check ilm flag to indicate whether t_xmin/t_xmax is xid or ilm time)+ | ctid:(block 0/0, offset 1) + | t_infomask: HEAP_XMAX_INVALID HEAP_HAS_NO_UID + | t_infomask2: Attrs Num: 1 + | t_hoff: 24 + | t_bits: NNNNNNNN + | Summary (1 total): 1 normal, 0 unused, 0 dead + | + | Normal Heap Page, special space is 0 + | + | (1 row)- gs_seg_get_spc_location(tablespace_name NAME, bucketnode INTEGER, head_block_id BIGINT, block_id BIGINT)
Description: Calculates the physical location given a segment and logical page number. Only an administrator can query the information.
Parameter description
Name
Type
Description
tablespace_name
NAME
Tablespace to which a segment belongs.
bucketnode
INTEGER
- 0 to 1023 indicate the bucket nodes of a hash bucket table.
- 1024 indicates the bucket node of a segment-page ordinary table.
- 1025 indicates the bucket node of a segment-page global temporary table.
- 1026 indicates the bucket node of a segment-page unlogged table.
- 1027 indicates the bucket node of a segment-page local temporary table.
head_block_id
BIGINT
Page number of a segment header.
block_id
BIGINT
Logical page number.
Return value description
Name
Type
Description
extent_id
INTEGER
Logical extent number of the logical page.
extent_size
INTEGER
Size of the logical extent where the logical page is located.
file_id
INTEGER
ID of the data file where the physical page is located.
file_block_id
BIGINT
Offset page number of the physical page in the data file.
For example, perform the following operations after creating a page-based ordinary table in the tablespace and inserting data:
gaussdb=# SELECT * FROM gs_seg_get_spc_location('pg_default', 1024, 4157, 0); extent_id | extent_size | file_id | file_block_id -----------+-------------+---------+--------------- 0 | 8 | 2 | 4157 (1 row) - gs_seg_get_spc_location(relid OID, bucketnode INTEGER, block_id BIGINT, partition BOOLEAD DEFAULT FALSE, forknum INTEGER DEFAULT 0)
Description: Calculates the physical location given a segment and logical page number. Only an administrator can query the information.
Parameter description
Name
Type
Description
relid
OID
Segment object ID.
bucketnode
INTEGER
- 0 to 1023 indicate the bucket nodes of a hash bucket table.
- 1024 indicates the bucket node of a segment-page ordinary table.
- 1025 indicates the bucket node of a segment-page global temporary table.
- 1026 indicates the bucket node of a segment-page unlogged table.
- 1027 indicates the bucket node of a segment-page local temporary table.
block_id
BIGINT
Logical page number.
partition
BOOLEAD DEFAULT FALSE
Specifies whether the segment object is a partition. The default value is FALSE.
forknum
INTEGER DEFAULT 0
Fork of a segment object. The default value is 0.
Value range:- 0: main fork.
- 1: FSM fork.
- 2: VM fork.
Return value description
Name
Type
Description
extent_id
INTEGER
Logical extent number of the logical page.
extent_size
INTEGER
Size of the logical extent where the logical page is located.
file_id
INTEGER
ID of the data file where the physical page is located.
file_block_id
BIGINT
Offset page number of the physical page in the data file.
In the following example, relid must be a valid OID of a multipart page object, and the object must have data:
gaussdb=# SELECT * FROM gs_seg_get_spc_location(24578,1024,0); extent_id | extent_size | file_id | file_block_id -----------+-------------+---------+--------------- 0 | 8 | 2 | 4157 (1 row) - gs_seg_get_location(block_id BIGINT, as_extent BOOLEAN DEFAULT FALSE)
Description: Calculates the physical location given a segment and logical page number. Only an administrator can query the information.
Parameter description
Name
Type
Description
block_id
BIGINT
Logical page number.
as_extent
BOOLEAN DEFAULT FALSE
Specifies whether the block_id parameter is an extent number. The default value is FALSE.
Return value description
Name
Type
Description
extent_id
BIGINT
Extent number.
extent_size
INTEGER
Extent size.
extent_offset
INTEGER
Extent offset block number.
level0_slots_idx
INTEGER
Index of the extent in the level-0 slot array in the segment header.
level1_slots_idx
INTEGER
Index of the extent in the level-1 slot array in the segment header.
level1_page_offset
INTEGER
Offset of the extent on the level-1 slot page in the segment header.
segment_blocks
BIGINT
Number of pages containing this page or extended segments.
relative_fno
INTEGER
Number of the relative file that contains this page or extent.
Example:
gaussdb=# SELECT * FROM gs_seg_get_location(4157); extent_id | extent_size | extent_offset | level0_slots_idx | level1_slots_idx | level1_page_offset | segment_blocks | relative_fno -----------+-------------+---------------+------------------+------------------+--------------------+----------------+-------------- 47 | 128 | 61 | 47 | | | 4158 | 3 (1 row) - gs_seg_get_segment_layout()
Description: Outputs the static segment layout. Only an administrator can query the information.
Return value description
Name
Type
Description
version
TEXT
Segment-page version. The default value is 1.0.
section_id
INTEGER
ID of the data section divided by a segment.
section_type
TEXT
Extent type of the segment data section.
Value range:- meta: segment header.
- data: data.
extent_size
INTEGER
Extent size. The unit is byte.
extent_page_count
INTEGER
Number of extent pages.
extent_count_start
BIGINT
Start extent number.
extent_count_end
BIGINT
End extent number.
total_size
BIGINT
Size of the segment data section. The unit is byte.
Example:
gaussdb=# SELECT * FROM gs_seg_get_segment_layout(); version | section_id | section_type | extent_size | extent_page_count | extent_count_start | extent_count_end | total_size ---------+------------+--------------+-------------+-------------------+--------------------+------------------+---------------- 1.0 | 1 | meta | 8192 | 1 | 0 | 0 | 8192 1.0 | 2 | data | 65536 | 8 | 1 | 16 | 1048576 1.0 | 3 | data | 1048576 | 128 | 17 | 143 | 134217728 1.0 | 4 | data | 8388608 | 1024 | 144 | 255 | 1073741824 1.0 | 5 | data | 33554432 | 4096 | 256 | 1025255 | 34394366541824 (5 rows) - gs_seg_get_datafile_layout()
Description: Queries the static layout of data files 1 to 5. Only an administrator can query the information.
Return value description
Name
Type
Description
version
TEXT
Segment-page version. The default value is 1.0.
seg_storage_type
TEXT
- segment indicates common segment-page data.
- hashbucket indicates hash bucket data.
file_id
INTEGER
Data file ID.
section_id
INTEGER
Data section ID of a data file.
section_type
TEXT
Type of the data file section.
Value range:
- file_header indicates the file header.
- spc_header indicates the space header.
- map_header indicates the mapping header.
- map_pages indicates the mapping page.
- ip_pages(inverse pointer pages) indicates the reverse pointer page.
- data_pages indicates the data page.
page_start
BIGINT
Start page number of the data section.
page_end
BIGINT
End page number of the data section.
page_count
BIGINT
Number of pages in the data section.
total_size
BIGINT
Size of the data section. The unit is byte.
Example:
gaussdb=# SELECT * FROM gs_seg_get_datafile_layout(); ... (There is a large amount of data. Only part of the data is displayed.)version | seg_storage_type | file_id | section_id | section_type | page_start | page_end | page_count | total_size ---------+------------------+---------+------------+--------------+--------------+--------------+-------------+----------------- 1.0 | segment | 1 | 0 | file_header | 0 | 0 | 1 | 8192 1.0 | segment | 1 | 1 | spc_header | 1 | 1 | 1 | 8192 1.0 | segment | 1 | 2 | map_header | 2 | 2 | 1 | 8192 1.0 | segment | 1 | 3 | map_pages | 3 | 66 | 64 | 524288 1.0 | segment | 1 | 4 | ip_pages | 67 | 4156 | 4090 | 33505280 1.0 | segment | 1 | 5 | data_pages | 4157 | 4147260 | 4143104 | 33940307968
- gs_seg_get_slice_layout(file_id INTEGER,bucketnode INTEGER, slice_id INTEGER)
Description: Outputs the static layout of a given data file fragment. Only an administrator can query the information.
Parameter description
Name
Type
Description
file_id
INTEGER
Data file ID.
bucketnode
INTEGER
- 0 to 1023 indicate the bucket nodes of a hash bucket table.
- 1024 indicates the bucket node of a segment-page ordinary table.
- 1025 indicates the bucket node of a segment-page global temporary table.
- 1026 indicates the bucket node of a segment-page unlogged table.
- 1027 indicates the bucket node of a segment-page local temporary table.
slice_id
INTEGER
Slice file ID.
Return value description
Name
Type
Description
version
TEXT
Segment-page version. The default value is 1.0.
section_id
INTEGER
Data section ID of a data file.
section_type
INTEGER
Type of the data file section.
Value range:
- file_header indicates the file header.
- spc_header indicates the space header.
- map_header indicates the mapping header.
- map_pages indicates the mapping page.
- ip_pages(inverse pointer pages) indicates the reverse pointer page.
- data_pages indicates the data page.
page_start
BIGINT
Start page number of the data section.
page_end
BIGINT
End page number of the data section.
page_count
BIGINT
Number of pages in the data section.
total_size
BIGINT
Size of the data section. The unit is byte.
Example:
gaussdb=# SELECT * FROM gs_seg_get_slice_layout(1,1024, 0); version | section_id | section_type | page_start | page_end | page_count | total_size ---------+------------+--------------+------------+----------+------------+------------ 1.0 | 0 | file_header | 0 | 0 | 1 | 8192 1.0 | 1 | spc_header | 1 | 1 | 1 | 8192 1.0 | 2 | map_header | 2 | 2 | 1 | 8192 1.0 | 3 | map_pages | 3 | 66 | 64 | 524288 1.0 | 4 | ip_pages | 67 | 4156 | 4090 | 33505280 1.0 | 5 | data_pages | 4157 | 131071 | 126915 | 1039687680 (6 rows) - gs_seg_get_segment(tablespace_name NAME, bucketnode INTEGER, head_block_id BIGINT)
Description: Outputs the segment header information of the segment header page in the segment header file of the tablespace. Only an administrator can query the information.
Parameter description
Name
Type
Description
tablespace_name
NAME
Tablespace to which a segment belongs.
bucketnode
INTEGER
- 0 to 1023 indicate the bucket nodes of a hash bucket table.
- 1024 indicates the bucket node of a segment-page ordinary table.
- 1025 indicates the bucket node of a segment-page global temporary table.
- 1026 indicates the bucket node of a segment-page unlogged table.
- 1027 indicates the bucket node of a segment-page local temporary table.
head_block_id
BIGINT
Page number of the segment header.
Return value description
Name
Type
Description
blocks
BIGINT
Number of logical pages of a segment.
total_blocks
BIGINT
Number of physical pages of a segment.
extents
INTEGER
Number of logical extents of a segment.
total_extents
INTEGER
Number of physical extents of a segment.
head_lsn
TEXT
Segment header LSN.
level0_slots
BIGINT[]
Level-0 slot array of segment extent mapping.
level1_slots
BIGINT[]
Level-1 slot array of segment extent mapping.
fork_head
BIGINT[]
Fork head array of a segment.
For example, perform the following operations after creating a segment-paged ordinary table:
gaussdb=# SELECT * FROM gs_seg_get_segment('pg_default', 1024, 4157); blocks | total_blocks | extents | total_extents | head_lsn | level0_slots | level1_slots | fork_head --------+--------------+---------+---------------+----------+--------------+--------------+---------------- 9 | 16 | 2 | 2 | 62211744 | {4157,4165} | {} | {4157,4158,-1} (1 row) - gs_seg_get_segment(relid OID, bucketnode INTEGER, partition BOOLEAD DEFAULT FALSE, forknum INTEGER DEFAULT 0)
Description: Outputs the corresponding segment header information based on relid and bucketnode. Only an administrator can query the information.
Parameter description
Name
Type
Description
relid
OID
Table OID.
bucketnode
INTEGER
- 0 to 1023 indicate the bucket nodes of a hash bucket table.
- 1024 indicates the bucket node of a segment-page ordinary table.
- 1025 indicates the bucket node of a segment-page global temporary table.
- 1026 indicates the bucket node of a segment-page unlogged table.
- 1027 indicates the bucket node of a segment-page local temporary table.
partition
BOOLEAN DEFAULT FALSE
Specifies whether the segment object is a partition. The default value is false.
Value range: bool, indicating whether the object corresponding to the input OID is a partition.
forknum
INTEGER DEFAULT 0
Fork number of a data file. The default value is 0.
Value range:
- 0: main fork.
- 1: FSM fork.
- 2: VM fork.
Return value description
Name
Type
Description
blocks
BIGINT
Number of logical pages of a segment.
total_blocks
BIGINT
Number of physical pages of a segment.
extents
INTEGER
Number of logical extents of a segment.
total_extents
INTEGER
Number of physical extents of a segment.
head_lsn
TEXT
Segment header LSN.
level0_slots
BIGINT[]
Level-0 slot array of segment extent mapping.
level1_slots
BIGINT[]
Level-1 slot array of segment extent mapping.
fork_head
BIGINT[]
Fork head array of a segment.
In the following example, relid must be a valid OID of a multipart page object:
gaussdb=# SELECT * FROM gs_seg_get_segment(16768, 1024); blocks | total_blocks | extents | total_extents | head_lsn | level0_slots | level1_slots | fork_head --------+--------------+---------+---------------+----------+--------------+--------------+---------------- 9 | 16 | 2 | 2 | 62211744 | {4157,4165} | {} | {4157,4158,4294967295} (1 row) - gs_seg_get_extents(tablespace_name NAME, bucketnode INTEGER, head_block_id BIGINT)
Description: Outputs all extents of the segment object on the segment header page in the segment header file of the tablespace, including segment head, fork head, level1 page in file 1 and data extents in files 2 to 5. Only an administrator can query the information.
Parameter description
Name
Type
Description
tablespace_name
NAME
Tablespace to which a segment belongs.
bucketnode
INTEGER
- 0 to 1023 indicate the bucket nodes of a hash bucket table.
- 1024 indicates the bucket node of a segment-page ordinary table.
- 1025 indicates the bucket node of a segment-page global temporary table.
- 1026 indicates the bucket node of a segment-page unlogged table.
- 1027 indicates the bucket node of a segment-page local temporary table.
head_block_id
BIGINT
Page number of the segment header.
Return value description
Name
Type
Description
extent_id
INTEGER
Logical extent number.
file_id
INTEGER
ID of the data file where the extent is located.
forknum
INTEGER
Segment fork.
Value range:- 0: main fork.
- 1: FSM fork.
- 2: VM fork.
block_id
BIGINT
Start page number in the data file where the extent is located.
blocks
INTEGER
Extent size.
Value range:
- 1 indicates file 1.
- 8 indicates file 2.
- 128 indicates file 3.
- 1024 indicates file 4.
- 4096 indicates file 5.
usage_type
TEXT
Usage type of an extent.
Value range:- segment head indicates the segment header.
- fork head indicates the fork header.
- level1 page indicates the level-1 page.
- data extent indicates data extents.
For example, perform the following operations after creating a segment-page ordinary table in the tablespace:
gaussdb=# SELECT * FROM gs_seg_get_extents('pg_default', 1024, 4157); extent_id | file_id | forknum | block_id | blocks | usage_type -----------+---------+---------+----------+--------+-------------- | 1 | 0 | 4157 | 1 | segment head 0 | 2 | 0 | 4157 | 8 | data extent 1 | 2 | 0 | 4165 | 8 | data extent (3 rows) - gs_seg_get_extents(relid OID, bucketnode INTEGER, partition BOOLEAD DEFAULT FALSE, forknum INTEGER DEFAULT 0)
Description: Outputs all extents of the segment object on the segment header page in the corresponding segment header file, including segment head, fork head, level1 page in file 1 and data extents in files 2 to 5. Only an administrator can query the information.
Parameter description
Name
Type
Description
relid
OID
Table OID.
bucketnode
INTEGER
- 0 to 1023 indicate the bucket nodes of a hash bucket table.
- 1024 indicates the bucket node of a segment-page ordinary table.
- 1025 indicates the bucket node of a segment-page global temporary table.
- 1026 indicates the bucket node of a segment-page unlogged table.
- 1027 indicates the bucket node of a segment-page local temporary table.
partition
BOOLEAN DEFAULT FALSE
Specifies whether the segment object is a partition. The default value is false.
Value range: bool, indicating whether the object corresponding to the input OID is a partition.
forknum
INTEGER DEFAULT 0
Fork number of a data file. The default value is 0.
Value range:
- 0: main fork.
- 1: FSM fork.
- 2: VM fork.
Return value description
Name
Type
Description
extent_id
INTEGER
Logical extent number.
file_id
INTEGER
ID of the data file where the extent is located.
forknum
INTEGER
Segment fork.
Value range:
- 0: main fork.
- 1: FSM fork.
- 2: VM fork.
block_id
BIGINT
Start page number in the data file where the extent is located.
blocks
INTEGER
Extent size.
Value range:
- 1 indicates file 1.
- 8 indicates file 2.
- 128 indicates file 3.
- 1024 indicates file 4.
- 4096 indicates file 5.
usage_type
TEXT
Usage type of an extent.
Value range:
- segment head indicates the segment header.
- fork head indicates the fork header.
- level1 page indicates the level-1 page.
- data extent indicates data extents.
In the following example, relid must be a valid OID of a multipart page object:
gaussdb=# SELECT * FROM gs_seg_get_extents(16768, 1024); extent_id | file_id | forknum | block_id | blocks | usage_type -----------+---------+---------+----------+--------+-------------- | 1 | 0 | 4157 | 1 | segment head 0 | 2 | 0 | 4157 | 8 | data extent 1 | 2 | 0 | 4165 | 8 | data extent (3 rows) - gs_seg_free_spc_remain_segment(tablespace_name NAME, head_file_id INTEGER, bucketnode INTEGER, head_block_id BIGINT)
Description: Releases the page occupied by the segment page-based residual segment in file 1 in a specified tablespace. You can query residual segments in the GS_SEG_SPC_REMAIN_SEGMENTS view. Only an administrator can query the information. This query can be executed only on the primary node.
- This function has a defect and is planned to be reconstructed in later versions to completely solve the residual segment-page problem. This function is an offline segment-page clearing method.
- To ensure the consistency between the queried residual segments and residual extents and the consistency of residual clearing, this function and the GS_SEG_SPC_REMAIN_SEGMENTS view must be executed in the DDL-\DML-restricted state. The current version does not provide the DML/DDL restriction capability. Therefore, when using this feature, ensure that the operating environment is in the DDL-\DML-restricted state.
- This function can be used only when enable_segment_remain_cleanup is set to off. For details about how to enable it, see "Configuring Running Parameters > GUC Parameters > Developer Options" in Administrator Guide.
Parameter description
Name
Type
Description
tablespace_name
NAME
Tablespace name.
head_file_id
INTEGER
ID of a data file in which a segment header of a segment-page-type residual segment is located. Value range: 1
bucketnode
INTEGER
- 0 to 1023 indicate the bucket nodes of a hash bucket table.
- 1024 indicates the bucket node of a segment-page ordinary table.
- 1025 indicates the bucket node of a segment-page global temporary table.
- 1026 indicates the bucket node of a segment-page unlogged table.
- 1027 indicates the bucket node of a segment-page local temporary table.
head_block_id
BIGINT
Page number of a segment header.
Return type: void
Example:
gaussdb=# SELECT * FROM gs_seg_free_spc_remain_segment('pg_default', 1, 1024, 4159); gs_seg_free_spc_remain_segment -------------------------------- (1 row) - gs_seg_free_spc_remain_extent(tablespace_name NAME, file_id INTEGER, bucketnode INTEGER, forknum INTEGER, block_id BIGINT)
Description: Releases residual segment-page-type isolated extents in a specified tablespace. Residual isolated extents can be queried in the GS_SEG_SPC_REMAIN_EXTENTS view. This function can also clear the segment header of the segment queried in the GS_SEG_SPC_REMAIN_SEGMENTS view. However, this action will expose other extents (such as fork head, level1 page, and data extent) in the segment where the cleared segment header is located in the GS_SEG_SPC_REMAIN_EXTENTS view. Only an administrator can query the information. This query can be executed only on the primary node.
- This function has a defect and is planned to be reconstructed in later versions to completely solve the residual segment-page problem. This function is an offline segment-page clearing method.
- To ensure the consistency between the queried residual segments and residual extents and the consistency of residual clearing, this function and the GS_SEG_SPC_REMAIN_EXTENTS view must be executed in the DDL- or DML-restricted state. The current version does not provide the DML/DDL restriction capability. Therefore, when using this feature, ensure that the operating environment is in the DDL-\DML-restricted state.
- This function can be used only when enable_segment_remain_cleanup is set to off. For details about how to enable it, see "Configuring Running Parameters > GUC Parameters > Developer Options" in Administrator Guide.
Parameter description
Name
Type
Description
tablespace_name
NAME
Tablespace name.
file_id
INTEGER
ID of the data file where the segment-page-type residual extent is located. Value range: files 1 to 5.
bucketnode
INTEGER
- 0 to 1023 indicate the bucket nodes of a hash bucket table.
- 1024 indicates the bucket node of a segment-page ordinary table.
- 1025 indicates the bucket node of a segment-page global temporary table.
- 1026 indicates the bucket node of a segment-page unlogged table.
- 1027 indicates the bucket node of a segment-page local temporary table.
forknum
INTEGER
Fork number of a data file.
Value range:- 0: main fork.
- 1: FSM fork.
- 2: VM fork.
block_id
BIGINT
Page number of a segment header.
Return type: void
Example:
gaussdb=# SELECT * FROM gs_seg_free_spc_remain_extent('pg_default', 1, 1024, 0, 4159); gs_seg_free_spc_remain_extent ------------------------------- (1 row) - gs_seg_get_datafiles(database_name NAME)
Description: Displays information about all data files of an instance. Only an administrator can query the information.
Parameter description
Name
Type
Description
database_name
NAME
Database name. The default value is current_database(), indicating the name of the current database.
Return value description
Name
Type
Description
file_name
TEXT
Data file name, for example, base/17467/2_fsm.
file_id
INTEGER
Data file ID. Value range: files 1 to 5.
bucketnode
INTEGER
- 0 to 1023 indicate the bucket nodes of a hash bucket table.
- 1024 indicates the bucket node of a segment-page ordinary table.
- 1025 indicates the bucket node of a segment-page global temporary table.
- 1026 indicates the bucket node of a segment-page unlogged table.
- 1027 indicates the bucket node of a segment-page local temporary table.
forknum
INTEGER
Fork type of a data file.
tablespace_name
NAME
Name of the tablespace to which a data file belongs.
contents
TEXT
Storage content of a data file.
Value range:- permanent: permanent.
- unlogged: no log.
- temporary: global temporary
- temporary2: local temporary
extent_size
INTEGER
Extent size of a data file.
meta_blocks
BIGINT
Number of allocated metadata pages of a data file.
data_blocks
BIGINT
Number of allocated data pages of a data file.
total_blocks
BIGINT
Total number of physical pages in a data file.
high_water_mark
BIGINT
High watermark of the number of pages used by a data file.
utilization
REAL
Percentage of used blocks to the total number of blocks, that is, (data_blocks + meta_blocks)/total_blocks.
For example, perform the following operations after creating a segment-paged table:
gaussdb=# SELECT * FROM gs_seg_get_datafiles(); file_name | file_id | bucketnode | forknum | tablespace_name | contents | extent_size | meta_blocks | data_blocks | total_blocks | high_water_mark | utilization --------------+---------+------------+---------+-----------------+-----------+-------------+-------------+-------------+--------------+-----------------+------------- base/15949/1 | 1 | 1024 | 0 | pg_default | permanent | 1 | 4157 | 1 | 16384 | 1048702976 | 2.24208e-44 base/15949/2 | 2 | 1024 | 0 | pg_default | permanent | 8 | 4157 | 8 | 16384 | 1048717312 | 2.24208e-44 (2 rows) - gs_seg_get_spc_extents(tablespace_name NAME, file_id INTEGER, bucketnode INTEGER, forknum INTEGER, skip_unused BOOLEAN DEFAULT TRUE)
Description: Obtains all extent information of a specified tablespace. Only an administrator can query the information.
Parameter description
Name
Type
Description
tablespace_name
NAME
Tablespace name.
file_id
INTEGER
Data file ID.
bucketnode
INTEGER
- 0 to 1023 indicate the bucket nodes of a hash bucket table.
- 1024 indicates the bucket node of a segment-page ordinary table.
- 1025 indicates the bucket node of a segment-page global temporary table.
- 1026 indicates the bucket node of a segment-page unlogged table.
- 1027 indicates the bucket node of a segment-page local temporary table.
forknum
INTEGER
Data file fork.
Value range:- 0: main fork.
- 1: FSM fork.
- 2: VM fork.
skip_unused
BOOLEAN DEFAULT TRUE
Specifies whether to output only allocated extents. The default value is TRUE, indicating that only allocated extents are output.
Return value description
Name
Type
Description
block_id
BIGINT
Start page number of a data extent.
blocks
INTEGER
Data extent size.
Value range:- 1 indicates file 1.
- 8 indicates file 2.
- 128 indicates file 3.
- 1024 indicates file 4.
- 4096 indicates file 5.
contents
TEXT
Stores content.
Value range:- permanent: permanent.
- unlogged: no log.
- temporary: global temporary.
- temporary2: local temporary.
in_used
TEXT
Specifies whether a resource has been allocated.
Value range:- Y: allocated.
- N: not allocated.
mapblock_location
TEXT
Position of the extent in the map block. Format: (page_id, offset).
head_file_id
INTEGER
ID of the data file where the segment header is located.
head_block_id
BIGINT
Page number of the segment header.
usage_type
TEXT
Usage type of an extent.
Value range:- segment head indicates the segment header.
- fork head indicates the fork header.
- level1 page indicates the level-1 page.
- data extent indicates data extents.
remain_flag
TEXT
Specifies whether it is a residual extent after the SHRINK operation.
Value range:- Y: residual extent upon SHRINK.
- N: not a residual extent upon SHRINK.
special_data
INTEGER
Special data section of the reverse pointer corresponding to an extent.
ipblock_location
TEXT
Position of the reverse pointer corresponding to an extent. Format: (block_id, offset).
Example:
gaussdb=# SELECT * FROM gs_seg_get_spc_extents('pg_default', 1,1024, 0); block_id | blocks | contents | in_used | mapblock_location | head_file_id | head_block_id | usage_type | remain_flag | special_data | ipblock_location ----------+--------+-----------+---------+-------------------+--------------+---------------+--------------+-------------+--------------+------------------ 4157 | 1 | permanent | Y | (4157,0) | 1 | 4157 | segment head | N | 0 | (67,0) 4158 | 1 | permanent | Y | (4157,1) | 1 | 4158 | fork head | N | 1 | (67,1) (2 rows)
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