Gerhard Wiesinger wrote:
Hello,
I'd like to understand the PostgreSQL internals in "backup mode".
When I understood it correctly pg_start_backup() make a checkpoint and
stops writing to the data/ directory except the WAL.
All new transaction go into WAL which is also logical. But how is data
consistency done when the written/changed blocks don't fit into the
buffer cache?
The data isn't kept consistent. Which is why you need the WAL. Restoring
from a PITR backup is basically the same idea as recovering from a
crash. Any blocks that might have been updated since you called
pg_start_backup() will be rewritten from the WAL.
--
Richard Huxton
Archonet Ltd
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