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Add support for coordinating record typmods among parallel workers.

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Tuples can have type RECORDOID and a typmod number that identifies a blessed
TupleDesc in a backend-private cache.  To support the sharing of such tuples
through shared memory and temporary files, provide a typmod registry in
shared memory.

To achieve that, introduce per-session DSM segments, created on demand when a
backend first runs a parallel query.  The per-session DSM segment has a
table-of-contents just like the per-query DSM segment, and initially the
contents are a shared record typmod registry and a DSA area to provide the
space it needs to grow.

State relating to the current session is accessed via a Session object
reached through global variable CurrentSession that may require significant
redesign further down the road as we figure out what else needs to be shared
or remodelled.

Author: Thomas Munro
Reviewed-By: Andres Freund
Discussion: https://postgr.es/m/CAEepm=0ZtQ-SpsgCyzzYpsXS6e=kZWqk3g5Ygn3MDV7A8dabUA@mail.gmail.com
This commit is contained in:
Andres Freund
2017-09-14 19:59:21 -07:00
parent 9b6cb4650b
commit cc5f81366c
12 changed files with 948 additions and 39 deletions
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8
src/backend/storage/lmgr/lwlock.c
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@@ -494,7 +494,7 @@ RegisterLWLockTranches(void)
if (LWLockTrancheArray == NULL)
{
LWLockTranchesAllocated = 64;
LWLockTranchesAllocated = 128;
LWLockTrancheArray = (char **)
MemoryContextAllocZero(TopMemoryContext,
LWLockTranchesAllocated * sizeof(char *));
@@ -510,6 +510,12 @@ RegisterLWLockTranches(void)
"predicate_lock_manager");
LWLockRegisterTranche(LWTRANCHE_PARALLEL_QUERY_DSA,
"parallel_query_dsa");
LWLockRegisterTranche(LWTRANCHE_SESSION_DSA,
"session_dsa");
LWLockRegisterTranche(LWTRANCHE_SESSION_RECORD_TABLE,
"session_record_table");
LWLockRegisterTranche(LWTRANCHE_SESSION_TYPMOD_TABLE,
"session_typmod_table");
LWLockRegisterTranche(LWTRANCHE_TBM, "tbm");
/* Register named tranches. */