On 1 November 2018 at 04:40, John Naylor <jcnay...@gmail.com> wrote: > Thanks for doing this. I haven't looked at the rendered output yet, > but I have some comments on the content. > > + <entry>Maximum Relation Size</entry> > + <entry>32 TB</entry> > + <entry>Limited by 2^32 pages per relation</entry> > > I prefer "limited to" or "limited by the max number of pages per > relation, ...". I think pedantically it's 2^32 - 1, since that value > is used for InvalidBlockNumber. More importantly, that seems to be for > 8kB pages. I imagine this would go up with a larger page size. Page > size might also be worth mentioning separately. Also max number of > relation file segments, if any.
Thanks for looking at this. I've changed this and added mention of BLKSIZE. I was a bit unclear on how much internal detail should go into this. > + <entry>Maximum Columns per Table</entry> > + <entry>250 - 1600</entry> > + <entry>Depending on column types. (More details here)</entry> > > Would this also depend on page size? Also, I'd put this entry before this one: > > + <entry>Maximum Row Size</entry> > + <entry>1600 GB</entry> > + <entry>Assuming 1600 columns, each 1 GB in size</entry> > > A toast pointer is 18 bytes, according to the docs, so I would guess > the number of toasted columns would actually be much less? I'll test > this on my machine sometime (not 1600GB, but the max number of toasted > columns per tuple). I did try a table with 1600 text columns then inserted values of several kB each. Trying with BIGINT columns the row was too large for the page. I've never really gotten a chance to explore these limits before, so I guess this is about the time. > + <entry>Maximum Identifier Length</entry> > + <entry>63 characters</entry> > + <entry></entry> > > Can this be increased with recompiling, if not conveniently? Yeah. I added a note about that. > + <entry>Maximum Indexed Columns</entry> > + <entry>32</entry> > + <entry>Can be increased by recompiling > <productname>PostgreSQL</productname></entry> > > How about the max number of included columns in a covering index? Those are included in the limit. I updated the text. >> I'm not so sure about detailing limits of GUCs since the limits of >> those are mentioned in pg_settings. > > Maybe we could just have a link to that section in the docs. That's likely a good idea. I was just unable to find anything better than the link to the pg_settings view. I've attached an updated patch, again it's just intended as an aid for discussions at this stage. Also included the rendered html. -- David Rowley http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & ServicesTitle: Appendix B. Database Limitations
Appendix B. Database Limitations
The following table describes the limits of PostgreSQL
Table B.1. PostgreSQL limitations
| Item | Limit | Comment |
|---|---|---|
| Maximum Database Size | Unlimited | |
| Maximum Number of Databases | Unlimited | |
| Maximum Relation Size | 32 TB | Limited to 2^32 - 1 pages per relation. Can be increased by
increasing BLCKSZ and recompiling
PostgreSQL |
| Maximum Columns per Table | 250 - 1600 | Depending on column types. (More details here) |
| Maximum Row Size | 1600 GB | Assuming 1600 columns, each 1 GB in size |
| Maximum Field Size | 1 GB | |
| Maximum Identifier Length | 63 characters | Can be increased by recompiling PostgreSQL |
| Maximum Rows per Table | Unlimited | |
| Maximum Indexes per Table | Unlimited | |
| Maximum Indexed Columns | 32 | Can be increased by recompiling PostgreSQL. Limit includes
any INCLUDE columns |
| Maximum Partition Keys | 32 | Can be increased by recompiling PostgreSQL |
| Maximum Relations per Database | Unlimited | |
| Maximum Partitions per Partitioned Relations | 268,435,456 | May be increased by using sub-partitioning |
v2-0001-Add-documentation-section-appendix-detailing-some.patch
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