Thread: Poverty Partitioning, include indexes
Hi all,
after decades I had a look at Postgres again, last week, due to V11.
Quite impressive, what has been achieved by the Postgres team since then.
Especially the Performance of recursive CTEs is superb,
especially in combination with window functions, lag, lead, row_number
Before Diving into the new partitioning methods, of which I assume, that they imply constraints on the used data model,
I observed, that a table is a file, e.g. data/base/1234/5678 . As soon the files size exceeds
1 Gig, more files will be created, 5678.1 for the next Gig, 5678.2 for another , and so on.
I had 10 of them for my CTE test table.
I brought down the pg-server, moved the ones with odd extension number to another disk and created
symbolic links in data/base/1234/ pointing to the moved files.
I restarted the pg-server, I was surprised, that everything still worked well, and I think, I noticed some speedup of my query. I assume, that is, because pg gathers the data of the files in parallel, and two disk can shuffle more data in the same time than one disk.
Is this a recommendable practice? Is it supported by postgres to do this by CREATE TABLE, Alter table?
Can somebody confirm the performance gain, does it even improve with more disks?
Oh. I spotted another highlight in V11, The Include indexes.
Tables with plenty of attributes actually speedup with ratio
number of all attributes / number of selected attributes
if an include index is build on the selected attributes + the PK.
with small index files and no impact on the Data model.
Simon Liesenfeld wrote: > Before Diving into the new partitioning methods, of which I assume, that they imply constraints on the used data model, > I observed, that a table is a file, e.g. data/base/1234/5678 . As soon the files size exceeds > 1 Gig, more files will be created, 5678.1 for the next Gig, 5678.2 for another , and so on. > I had 10 of them for my CTE test table. > > I brought down the pg-server, moved the ones with odd extension number to another disk and created > symbolic links in data/base/1234/ pointing to the moved files. > I restarted the pg-server, I was surprised, that everything still worked well, and I think, > I noticed some speedup of my query. I assume, that is, because pg gathers the data of the files > in parallel, and two disk can shuffle more data in the same time than one disk. > > Is this a recommendable practice? Is it supported by postgres to do this by CREATE TABLE, Alter table? > Can somebody confirm the performance gain, does it even improve with more disks? No, it is not recommended, it will break your database. Don't manually mess with the table files. If you want to place some partitions on a different disk, create a tablespace on that disk and ALTER the tables to move them there. Depending on your system and query, placing different partitions on different disks can improve your performance, particularly if I/O is the bottleneck. Yours, Laurenz Albe -- Cybertec | https://www.cybertec-postgresql.com