I've got a postgres database which I recently vacuumed. I understand that process marks space as available for future use, but for the most part does not return it to the OS.
I need to track how close I am to using up that available "slack space" so I can ensure the entire database does not start to grow again.
Is there a way to see how much empty space the database has inside it?
I'd prefer to just do a VACUUM FULL and monitor disk consumption, but I can't lock the table for a prolonged period, nor do I have the disk space.
Running version 13 on headless Ubuntu if that's important.
Just like internal free space is not given back to the OS, it also isn't shared between tables or other relations (like indexes). So having freespace in one table isn't going to help if a different table is the one growing. You can use pg_freespacemap to get a fast approximate answer for each table, or pgstattuple for more detailed data.
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I have a couple of tables in a PostgreSQL database which are used very frequently (for Insert/Delete purposes). Sometimes, their size of the tables grow up to GB's. How do I reclaim the disk space from these tables without locking them. These tables need to be used almost all the times so I can't afford getting them locked. VACUUM FULL reclaims the disk space however locks the table so I can't use FULL option.
Can someone please suggest a way?
Thanks
Often you can avoid the problem by configuring autovacuum sufficiently aggressive that it can keep up with the change rate.
If that doesn't do the trick, or if you have regular mass DELETEs, look into a tool like pg_squeeze or pg_repack.
I have a CloudSQL instance (PostgreSQL) with 112.7 GB data in it:
I wanted to transfer the data in this instance to another one.
I did an export first and then created another instance and imported the data there.
All went good. However, the resulting instance has less storage usage, only 102 GB:
No errors found in the logs. I am wondering where the 10GB data went.
Is this expected?
This is caused due to fragmentation in the table. In the case of MySQL:
One symptom of fragmentation is that a table takes more space than it
“should” take. How much that is exactly, is difficult to determine.
All InnoDB data and indexes are stored in B-trees, and their fill
factor may vary from 50% to 100%. Another symptom of fragmentation is
that a table scan such as this takes more time than it “should”
take:...
In the PostgreSQL docs (see the section 23.1.2. Recovering Disk Space), it is explained:
In PostgreSQL, an UPDATE or DELETE of a row does not immediately
remove the old version of the row. This approach is necessary to gain
the benefits of multiversion concurrency control (MVCC, see Chapter
13): the row version must not be deleted while it is still potentially
visible to other transactions. But eventually, an outdated or deleted
row version is no longer of interest to any transaction. The space it
occupies must then be reclaimed for reuse by new rows, to avoid
unbounded growth of disk space requirements. This is done by running
VACUUM.
Also read the Vacuum the Dirt out of Your Database doc in order to see steps to overcome this.
Hope this helps.
I ran a vaccum on the tables of my database and it appears it is not helping me. For example I have a huge table and when I run vacuum on it, it returns there are 87887889 dead row versions that can not be deleted
My question is how to get rid of these dead rows
You have two basic options if a routine vacuum is insufficient. Both require a full table lock.
VACUUM FULL. This requires no additional disk space but takes a while to complete.
CLUSTER. This rewrites a table in a physical order optimized for a given index. It requires additional space to do the rewrite, but is much faster.
In general I would recommend using CLUSTER during a maintenance window if disk space allows.
I use PostgreSQL on an embedded system with limited drive space. Now the DB-drive is full. When I delete data, it doesn't seem to free up any space. I tried to VACUUM FULL, but that requires space. So does deleting the last remaining index.
Any ideas on how to free up space without randomly deleting stuff? I can afford to lose some of the data from back when, but I can't seem to actually do it, since there isn't enough space to VACUUM FULL.
PostgreSQL uses MVCC model which means that deleted records mark their space as free (after the transaction which deleted them had been committed) but it is still reserved by the table.
Prior to PostgreSQL 9.0, VACUUM FULL used to move the data inside the table without need for additional space.
In PostgreSQL 9.0, behavior of VACUUM FULL had changed and now it requires additional space for the full copy of the table.
You may try to drop the indexes from the tables and vacuum them one by one, starting from the least one.
The easiest answer at this point would be to dump the database to a different drive/computer (for instance, using pg_dump, or pg_dumpall if you have more than one db, and keeping in mind things like Large Objects that need special backup/restore processes) then drop and recreate the database.
If there's a tiny bit of space left, you might try vacuum full smallesttable, which might be able to finish and free up some space to vacuum the next smallest table, and so on.
If you end up filling the drive completely, the database server will probably refuse to start and you won't be able to do either of those. In that case, you could move the entire data directory to another computer with the same CPU architecture and more disk space, then start postgresql there to perform the vacuum.
In certain situations VACUUM (not full) can reclaim some disk space. (I think it will return pages that are totally dead to the OS.) That might free up enough space to begin with the VACUUM FULL. But it's not a good idea to let one table grow to more than the amount of disk free space.
I have a 9 million row table. I figured out that a large amount of it (around 90%) can be freed up. What actions are needed after the cleanup? Vacuum, reindex etc.
If you want to free up space on the file system, either VACUUM FULL or CLUSTER can help you. You may also want to run ANALYZE after these, to make sure the planner has up-to-date statistics but this is not specifically required.
It is important to note using VACUUM FULL places an ACCESS EXCLUSIVE lock on your table(s) (blocking any operation, writes & reads), so you probably want to take your application offline for the duration.
In PostgreSQL 8.2 and earlier, VACUUM FULL is probably your best bet.
In PostgreSQL 8.3 and 8.4, the CLUSTER command was significantly improved, so VACUUM FULL is not recommended -- it's slow and it will bloat your indexes. `CLUSTER will re-create indexes from scratch and without the bloat. In my experience, it's usually much faster too. CLUSTER will also sort the whole physical table using an index, so you must pick an index. If you don't know which, the primary key will work fine.
In PostgreSQL 9.0, VACUUM FULL was changed to work like CLUSTER, so both are good.
It's hard to make predictions, but on a properly tuned server with commodity hardware, 9 million rows shouldn't take longer than 20 minutes.
See the documentation for CLUSTER.
PostgreSQL wiki about VACUUM FULL and recovering dead space
You definitely want to run a VACUUM, to free up that space for future inserts. If you want to actually reclaim that space on disk, making it available to the OS, you'll need to run VACUUM FULL. Keep in mind that VACUUM can run concurrently, but VACUUM FULL requires an exclusive lock on the table.
You will also want to REINDEX, since the indexes will remain bloated even after the VACUUM runs. If possible, a much faster way to do this is to drop the index and create it again from scratch.
You'll also want to ANALYZE, which you can just combine with the VACUUM.
See the documentation for more info.
Hi
Don't it be more optimal to create a temporary table with 10% of needed records. Then drop original table and rename temporary to original ...
I'm relatively new to the world of Postgres, but I understand VACUUM ANALYZE is recommended. I think there's also a sub-option which just frees up space. I found reindex useful as well when doing batch inserts or deletes. Yes I've been working with tables with a similar number of rows, and the speed increase is very noticeable (UBuntu, Core 2 Quad)