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In this talk, we will cover about Dynamic Shared Memory Segments - an alternative to the main shared memory , where memory can be requested even after PG startup.

Problem -

PG uses shared memory for inter-process communication among processes that need to access and share data with each other. But, the postmaster allows requesting any bytes in the main shared memory, only during PG startup. So, any operations that need some memory once the PG is up, can’t use the main shared memory.

Solution -

To tackle this problem, dynamic shared memory segments were introduced in Postgres 9.4 . The talk will primarily focus on -

1. Memory allocation and subsequent access in DSM
2. How is it different from main shared memory - since DSM structures are not mapped to the same address space in each process
3. Nuances due to #2 above - use of offsets instead of pointers in DSM structures
4. Application and use-cases
   • Parallel query execution
   • Creating extensions that need on-demand memory

Audience -

This talk will be primarily useful for developers building on top of OSS PG - who can use this knowledge to build custom extensions , fine-tune parallel query execution based on their needs, etc.

Impact -

Attendees will leave with a solid understanding of a core kernel topic that can be leveraged in varied ways, from building high-performance, parallel-aware extensions to more effectively diagnosing and tuning complex query plans.