Currently, chunk indexes are always created in the tablespace of the
index on the main table (which could be none/default one), even if the
chunks themselves are created in different tablespaces. This is
problematic in a multi-disk setting where each disk is a separate
tablespace where chunks are placed. The chunk indexes might exhaust
the space on the common (often default tablespace) which might not
have a lot of disk space. This also prohibits the database, including
index storage to grow by adding new tablespaces.
Instead, chunk indexes are now created in the "next" tablespace after
that of their chunks to both spread indexes across tablespaces and
avoid colocating indexes with their chunks (for I/O throughput
reasons). To optionally avoid this spreading, one can pin chunk
indexes to a specific tablespace by setting an explicit tablespace on
a main table index.
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