英文:
why do we need a TABLESPACE_VERSION_DIRECTORY in PostgreSQL's tablespace?
问题
我找到了位于像pg_tblspc/16384/PG_11_201809051/13888/16385这样的目录下的文件，并发现它们来自TABLESPACE_VERSION_DIRECTORY宏。
但是，我不明白为什么我们需要这个级别的目录。我们不能只使用pg_tblspc/16384/13888/16385吗？有什么好处？如果不使用它会发生什么？它与表空间的符号链接有关吗？
英文:
I found the files in pg_tblspc under directories like pg_tblspc/16384/PG_11_201809051/13888/16385
, and I found they comes from the TABLESPACE_VERSION_DIRECTORY macro.
However, I don't understand why we need this level of directory. Can't we just use pg_tblspc/16384/13888/16385? What is the benefit? What will happen if we don't use it? Does it have any relation to the symbol link of tablespace?
答案1
得分: 0
TABLESPACE_VERSION_DIRECTORY 的目的是为了避免意外使用错误版本的 PostgreSQL 数据文件。在主数据目录中，PG_VERSION 文件已经实现了这个目的。TABLESPACE_VERSION_DIRECTORY 显著体现其作用的一个明显场景是在使用 pg_upgrade 进行升级时：由于表空间目录位置保持不变，不同版本的文件仅通过不同的 TABLESPACE_VERSION_DIRECTORY 区分。
英文:
The purpose of TABLESPACE_VERSION_DIRECTORY is to avoid accidentally using data files with a wrong version of PostgreSQL. In the main data directory, that purpose is served by the PG_VERSION file. One very obvious place where the TABLESPACE_VERSION_DIRECTORY shows its power is during an upgrade with pg_upgrade: since the tablespace directory location stays the same, the files from the different versions are only distinguished by the different TABLESPACE_VERSION_DIRECTORY.
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