mirror of
https://github.com/timescale/timescaledb.git
synced 2025-05-17 02:53:51 +08:00
a38332a8af
Add support for dumping and restoring hypertables that have chunks that use the Hypercore TAM. Dumping a Hypercore table requires special consideration because its data is internally stored in two separate relations: one for compressed data and one for non-compressed data. The TAM returns data from both relations, but they may be dumped as separate tables. This risks dumping the compressed data twice: once via the TAM and once via the compressed table in compressed format. The `pg_dump` tool uses `COPY TO` to create dumps of each table, and, to avoid data duplication when used on Hypercore tables, this change introduces a GUC that allows selecting one of these two behaviors: 1. A `COPY TO` on a Hypercore table returns all data via the TAM, including data stored in the compressed relation. A `COPY TO` on the internal compressed relation returns no data. 2. A `COPY TO` on a Hypercore returns only non-compressed data, while a `COPY TO` on the compressed relation returns compressed data. A `SELECT` still returns all the data as normal. The second approach is the default because it is consistent with compression when Hypercore TAM is not used. It will produce a `pg_dump` archive that includes data in compressed form (if data was compressed when dumped). Conversely, option (1) will produce an archive that looks identical to a dump from an non-compressed table. There are pros and cons of each dump format. A non-compressed archive is a platform-agnostic logical dump that can be restored to any platform and architecture, while a compressed archive includes data that is compressed in a platform-dependent way and needs to be restored to a compatible system. A test is added that tests both these settings and corresponding dumping and restoring.