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Commitd061ea2

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Adjust DSM and DSA slot usage constants.
When running a lot of large parallel queries concurrently, or a plan witha lot of separate Gather nodes, it is possible to run out of DSM slots.There are better solutions to these problems requiring architecturalredesign work, but for now, let's adjust the constants so that it's moredifficult to hit the limit.1. Previously, a DSA area would create up to four segments at each sizebefore doubling the size. After this commit, it will create only two ateach size, so it ramps up faster and therefore needs fewer slots.2. Previously, the total limit on DSM slots allowed for 2 per connection.Switch to 5 per connection.Also remove an obsolete nearby comment.Author: Thomas MunroReviewed-by: Robert Haas, Andres FreundDiscussion:https://postre.es/m/CA%2BhUKGL6H2BpGbiF7Lj6QiTjTGyTLW_vLR%3DSn2tEBeTcYXiMKw%40mail.gmail.com
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‎src/backend/storage/ipc/dsm.c

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@@ -45,13 +45,8 @@
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#definePG_DYNSHMEM_CONTROL_MAGIC0x9a503d32
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/*
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* There's no point in getting too cheap here, because the minimum allocation
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* is one OS page, which is probably at least 4KB and could easily be as high
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* as 64KB. Each currently sizeof(dsm_control_item), currently 8 bytes.
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*/
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#definePG_DYNSHMEM_FIXED_SLOTS64
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#definePG_DYNSHMEM_SLOTS_PER_BACKEND2
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#definePG_DYNSHMEM_SLOTS_PER_BACKEND5
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#defineINVALID_CONTROL_SLOT((uint32) -1)
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‎src/backend/utils/mmgr/dsa.c

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@@ -74,7 +74,7 @@
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* dsm.c's limits on total number of segments), or limiting the total size
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* an area can manage when using small pointers.
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*/
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#defineDSA_NUM_SEGMENTS_AT_EACH_SIZE4
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#defineDSA_NUM_SEGMENTS_AT_EACH_SIZE2
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/*
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* The number of bits used to represent the offset part of a dsa_pointer.

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