michalmuskala
Another small library today.
PersistentEts
Hex: persistent_ets | Hex
GitHub: GitHub - michalmuskala/persistent_ets · GitHub
Ets table backed by a persistence file.
The table is persisted using the :ets.file2tab/2 and :ets.tab2file/3 functions.
Table is to be created with PersistentEts.new/3 in place of :ets.new/2. After that all functions from :ets can be used like with any other table, except :ets.give_away/3 and :ets.delete/1 - replacement functions are provided in this module. The :ets.setopts/2 function to change the heir is not supported - the heir setting is leveraged by the persistence mechanism.
Like with regular ets table, the table is destroyed once the owning process (the one that called PersistentEts.new/3) dies, but the table data is persisted so it will be re-read when table is opened again.
Example
pid = spawn(fn ->
:foo = PersistentEts.new(:foo, "table.tab", [:named_table])
:ets.insert(:foo, [a: 1])
end)
Process.exit(pid, :diediedie)
PersistentEts.new(:foo, "table.tab", [:named_table])
[a: 1] = :ets.tab2list(:foo)
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michalmuskala
With Dets every operation (read or write) hits the disk. For many application such a performance penalty (compared to ets) is not acceptable. Furthermore Dets tables are limited to 2GB. Dets doesn’t support the
ordered_settable type either.With PersistentEts, the table remains in memory, so all read and write operations have the same performance they would have with pure ets. Only periodically the table state is saved to a file. There’s also no file limit, besides the memory and disk limitations. Since it’s a regular Ets table, all types are fully supported.
hubertlepicki
Could you highlight for us how it differs from DETS and why would someone choose one against another?
hubertlepicki
Copy paste that to readme now.
Last Post!
lessless
Thank you for insights!
I tried to look into the sources of
tab2filebut didn’t have enough patience to dig deep down into what they’re using there for file manipulationI just saw that they’re using message passing and that was enough for me to understand that there will definitely be overhead.