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Re: REINDEX vs VACUUM

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I don't think VACUUM FULL (copy the table, create new indices and other metadata all in one command) actually vacuums tables.  It's a misleading name.

Something like REBUILD TABLE would be a better name.

On 1/4/23 07:25, Rébeli-Szabó Tamás wrote:
Here is my understanding:

REINDEX recreates the index from scratch, using the data stored in the underlying table. It is the same as dropping and recreating the index manually, with regard to the impact on the index file. It can free up physical space in the file system. REINDEX will not vacuum the index.

VACUUM does many different things. One of them is vacuuming indexes (for the underlying table that is being vacuumed). VACUUM will remove index entries that are pointing to dead rows in the underlying table. VACUUM will not rebuild the entire index.

VACUUM recycles free index blocks (using FSM), but it does not (usually) free up space for the file system physically. VACUUM FULL does that.

VACUUM FULL will vacuum the index, but it will do it by making a copy of the index (file) and reorganizing its content in order to free up space physically. In that regard, it is like REINDEX. Both VACUUM FULL and REINDEX will block reads from the index during the process (by taking an ACCESS EXCLUSIVE lock).

Regards,

tamas

2022. 12. 31. 22:04 keltezéssel, Hao Zhang írta:
What is the difference between reindex and vacuum's impact on index file? I deleted an indexed row. Running either vacuum or reindex shows the index entry for the row is removed from the index page. I was under the impression that only reindex will remove dangling index entries. I am guessing that vacuum will not shrink the index file and will only add deleted index entries in the free space file for the index? But REINDEX is recreating the index file from scratch so it is like vacuum full for index?

Thanks



--
Born in Arizona, moved to Babylonia.





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