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Michael Paquier af720b4c50 Change custom wait events to use dynamic shared hash tables ... Currently, the names of the custom wait event must be registered for each backend, requiring all these to link to the shared memory area of an extension, even if these are not loaded with shared_preload_libraries. This patch relaxes the constraints related to this infrastructure by storing the wait events and their names in two dynamic hash tables in shared memory. This has the advantage to simplify the registration of custom wait events to a single routine call that returns an event ID ready for consumption: uint32 WaitEventExtensionNew(const char *wait_event_name); The caller of this routine can then cache locally the ID returned, to be used for pgstat_report_wait_start(), WaitLatch() or a similar routine. The implementation uses two hash tables: one with a key based on the event name to avoid duplicates and a second using the event ID as key for event lookups, like on pg_stat_activity. These tables can hold a minimum of 16 entries, and a maximum of 128 entries, which should be plenty enough. The code changes done in worker_spi show how things are simplified (most of the code removed in this commit comes from there): - worker_spi_init() is gone. - No more shared memory hooks required (size requested and initialization). - The custom wait event ID is cached in the process that needs to set it, with one single call to WaitEventExtensionNew() to retrieve it. Per suggestion from Andres Freund. Author: Masahiro Ikeda, with a few tweaks from me. Discussion: https://postgr.es/m/20230801032349.aaiuvhtrcvvcwzcx@awork3.anarazel.de		2 years ago
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src	Change custom wait events to use dynamic shared hash tables	2 years ago
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