|From:||Arthur Zakirov <a(dot)zakirov(at)postgrespro(dot)ru>|
|To:||Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>|
|Cc:||Andres Freund <andres(at)anarazel(dot)de>, Robert Haas <robertmhaas(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>|
|Subject:||Re: [PROPOSAL] Shared Ispell dictionaries|
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I've created the new commitfest entry since the previous entry was
closed with status "Returned with feedback":
I attached new version of the patch. There are changes only in
I added a reference counter to shared hash tables dictionary entries. It
is necessary to not face memory bloat. It is necessary to delete shared
hash table entries if there are a lot of ALTER and DROP TEXT SEARCH
Previous version of the patch had released unused DSM segments but left
shared hash table entries untouched.
There was refcnt before:
But I didn't fully understand how on_dsm_detach() works.
On 22.01.2019 22:17, Tomas Vondra wrote:
> I think there are essentially two ways:
> (a) Define max amount of memory available for shared dictionarires, and
> come up with an eviction algorithm. This will be tricky, because when
> the frequently-used dictionaries need a bit more memory than the limit,
> this will result in trashing (evict+load over and over).
> (b) Define what "unused" means for dictionaries, and unload dictionaries
> that become unused. For example, we could track timestamp of the last
> time each dict was used, and decide that dictionaries unused for 5 or
> more minutes are unused. And evict those.
> The advantage of (b) is that it adopts automatically, more or less. When
> you have a bunch of frequently used dictionaries, the amount of shared
> memory increases. If you stop using them, it decreases after a while.
> And rarely used dicts won't force eviction of the frequently used ones.
I'm working on the (b) approach. I thought about a priority queue
structure. There no such ready structure within PostgreSQL sources
except binaryheap.c, but it isn't for concurrent algorithms.
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