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Update layered_repository/README.md

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anastasia
2021-09-09 20:16:02 +03:00
committed by lubennikovaav
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docs/glossary.md
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@@ -36,6 +36,7 @@ Stateless Postgres node that stores data in pageserver.
### Garbage collection
The process of removing old on-disk layers that are not needed by any timeline anymore.
### Fork
Each of the separate segmented file sets in which a relation is stored. The main fork is where the actual data resides. There also exist two secondary forks for metadata: the free space map and the visibility map.
@@ -43,7 +44,7 @@ Each PostgreSQL fork is considered a separate relish.
### Layer
Each layer corresponds to one RELISH_SEG_SIZE slice of a relish in a range of LSNs.
Each layer corresponds to the specific version of a relish Segment in a range of LSNs.
There are two kinds of layers, in-memory and on-disk layers. In-memory
layers are used to ingest incoming WAL, and provide fast access
to the recent page versions. On-disk layers are stored as files on disk, and
@@ -122,6 +123,16 @@ One repository corresponds to one Tenant.
How much history do we need to keep around for PITR and read-only nodes?
### Segment (PostgreSQL)
NOTE: This is an overloaded term.
A physical file which stores data for a given relation. File segments are limited in size by a configuration value (typically 1 gigabyte), so if a relation exceeds that size, it is split into multiple segments.
### Segment (Layered Repository)
NOTE: This is an overloaded term.
Segment is a RELISH_SEG_SIZE slice of relish (defined by a SegmentTag).
### SLRU
SLRUs include pg_clog, pg_multixact/members, and