Hi Richard, I got side-tracked with other work, but am coming back to this now.
On Sun, Jan 15, 2017 at 5:50 PM, Richard Hipp <d...@sqlite.org> wrote: > On 1/15/17, Kim Gräsman <kim.gras...@gmail.com> wrote: >> >> 1) If I configure a global SQLite heap with SQLITE_CONFIG_HEAP, won't >> I just trade malloc heap fragmentation for SQLite private heap >> fragmentation? Or does SQLite's fragmentation-prevention strategy work >> well even in the face of multiple page sizes and connections? > > As described in the document that you read > (https://www.sqlite.org/malloc.html), if you keep your memory usage > below the Robson limit, then fragmentation will never be a problem. > Guaranteed. > > If you exceed the Robson limit, it is theoretically possible that > fragmentation could cause problems. But in practice, we don't > normally have issues. > >> >> 2) What happens if the configured heap is depleted? > > You get SQLITE_NOMEM errors. Use sqlite3_memory_used() to monitor > your memory utilization and raise alarms if it gets too high. And/or > call sqlite3_db_release_memory() to try to free up memory from caches > if you start to run low. Thanks, makes sense! We are having a hard time estimating needed memory up-front, and we can't afford SQLITE_NOMEM (we'd rather take slower allocation/fragmentation). Especially since our app has a mix of long-running and transient connections, it's hard for us to tell exactly how many, with what cache needs, will be running concurrently at any one time. One thing that we've been discussing internally, and can't find a definitive answer to: Why are these arenas/buffers global, and not associated with each connection? It seems to me making a big chunk malloc() to match cache size when opening a connection would make it easier for an application such as ours, where some connections come and go. I guess it could be more fragmentation-/OOM-prone but with a reasonable malloc implementation it feels like it would be more flexible without sacrificing much of the benefits. Thank you, - Kim _______________________________________________ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
