pgsql: Improve memory use in logical replication apply

Improve memory use in logical replication apply

Previously, the memory used by the logical replication apply worker for
processing messages would never be freed, so that could end up using a
lot of memory. To improve that, change the existing ApplyContext memory
context to ApplyMessageContext and reset that after every
message (similar to MessageContext used elsewhere). For consistency of
naming, rename the ApplyCacheContext to ApplyContext.

Author: Stas Kelvich <s(dot)kelvich(at)postgrespro(dot)ru>

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/489b96e80b96c0eda02575347654e87968f2f5f4

Modified Files
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src/backend/replication/logical/worker.c | 51 ++++++++++++++++---------------
src/backend/utils/mmgr/README | 11 +++++++
src/include/replication/worker_internal.h | 4 +--
3 files changed, 40 insertions(+), 26 deletions(-)