ADBDEV-6577: Use short-lived SPI contexts

[RekGRpth]

Use short-lived SPI contexts

diskquota uses long-lived SPI contexts in most places: at the beginning it
calls the SPI_connect function, which creates an SPI context and switches to
its use, then it does a lot of work, including SPI_execute, and only at the
very end it calls the SPI_finish function, which clears the SPI context. This
usage architecture is incorrect and can lead to memory leaks while the SPI
context is alive, because the SPI_execute function, for example, allocates
memory in it for parsing a SQL query. Correct use of SPI involves opening and
closing the SPI as close as possible, so that the SPI context is as short-lived
as possible. This patch adds new wrappers for connecting and disconnecting
functions from SPI and their usage, and moves the connection to SPI into
functions closer to making requests over SPI.

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[silent-observer]

Can you list the functions that opened SPI connection before this patch and after, and which contain which? As far as I can see

1. create_monitor_db_table (both before and after)
2. init_database_list (both before and after)
3. do_process_extension_ddl_message (both before and after)
4. worker_spi_get_extension_version (both before and after)
5. check_diskquota_state_is_ready (both before and after)
6. refresh_disk_quota_usage (removed)
   • load_table_size (added)
   • get_rel_oid_list (added)
   • delete_from_table_size_map (added)
   • insert_into_table_size_map (added)

[RekGRpth]

Can you list the functions that opened SPI connection before this patch and after, and which contain which? As far as I can see

1. `create_monitor_db_table` (both before and after)

2. `init_database_list` (both before and after)

3. `do_process_extension_ddl_message` (both before and after)

4. `worker_spi_get_extension_version` (both before and after)

5. `check_diskquota_state_is_ready` (both before and after)

6. `refresh_disk_quota_usage` (removed)
   
   * `load_table_size` (added)
   * `get_rel_oid_list` (added)
   * `delete_from_table_size_map` (added)
   * `insert_into_table_size_map` (added)

7. load_quotas (both before and after)

[silent-observer]

Can you add this to the description? At least the refresh_disk_quota_usage and functions called from it, since the behavior was changed

[RekGRpth]

since the behavior was changed

It's just the behavior that hasn't changed!

[RekGRpth]

Can you add this to the description?

added