sql: improve pg_table_is_visible performance#59880
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craig[bot] merged 1 commit intocockroachdb:masterfrom Feb 9, 2021
Merged
sql: improve pg_table_is_visible performance#59880craig[bot] merged 1 commit intocockroachdb:masterfrom
craig[bot] merged 1 commit intocockroachdb:masterfrom
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otan
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pkg/sql/sem/builtins/pg_builtins.go
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| "SELECT nspname FROM pg_catalog.pg_class c JOIN pg_catalog.pg_namespace n ON c.relnamespace=n.oid "+ | ||
| "WHERE c.oid=$1 AND nspname=ANY(current_schemas(true))", oid) | ||
| oid := tree.MustBeDOid(args[0]) | ||
| isVisibe, err := ctx.Planner.IsTableVisible(ctx.Context, ctx.SessionData.SearchPath, int64(oid.DInt)) |
pkg/sql/resolver.go
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| // IsTableVisible is part of the tree.EvalDatabase interface. | ||
| func (p *planner) IsTableVisible( | ||
| ctx context.Context, searchPath sessiondata.SearchPath, tableId int64, |
| return false, nil | ||
| } | ||
| iter := searchPath.Iter() | ||
| for scName, ok := iter.Next(); ok; scName, ok = iter.Next() { |
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do we need to check database too? what if db is in dropping state?
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uhh i guess not since it relies on search path.
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hmm actually my code won't work because you could have two schemas in different databases, but with the same name.
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i guess the old code had the same bug..
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HMMM though actually when cross-database references are fully banned, then we don't need to worry about it... (#55791)
otan
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Feb 8, 2021
pkg/sql/sem/tree/eval.go
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| // IsTableVisible checks if the table with the given ID belongs to a schema | ||
| // on the given sessiondata.SearchPath. | ||
| IsTableVisible(ctx context.Context, searchPath sessiondata.SearchPath, tableId int64) (bool, error) |
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RFAL -- i updated to explicitly account for cross-db references (and match the PG behavior) |
This is motivated by a query that Django makes in order to retrieve all the tables visible in the current session. The query uses the pg_table_is_visible function. Previously this was implemented by using the internal executor to inspect the pg_catalog. This was expensive because the internal executor does not share the same descriptor collection as the external context, so it ended up fetching every single table descriptor one-by-one. Now, we avoid the internal executor and lookup the table descriptor directly. There are other builtins that use the internal executor that may face the same problem. Perhaps an approach for the future is to allow builtin functions to be implemented using user-defined scalar functions. I added a benchmark that shows the original Django query performing a constant number of descriptor lookups with this new implementation. Previously, the same benchmark would make hundreds of roundtrips. Release note (performance improvement): Improve performance of the pg_table_is_visible builtin function.
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otan
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Feb 9, 2021
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tftr! bors r=otan |
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i mean bors r=otan |
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Build succeeded: |
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This is motivated by a query that Django makes in order to retrieve all
the tables visible in the current session. The query uses the
pg_table_is_visible function. Previously this was implemented by using
the internal executor to inspect the pg_catalog. This was expensive
because the internal executor does not share the same descriptor
collection as the external context, so it ended up fetching every single
table descriptor one-by-one.
Now, we avoid the internal executor and lookup the table descriptor
directly.
There are other builtins that use the internal executor that may face
the same problem. Perhaps an approach for the future is to allow builtin
functions to be implemented using user-defined scalar functions.
I added a benchmark that shows the original Django query performing a
constant number of descriptor lookups with this new implementation.
fixes #57924
Release note (performance improvement): Improve performance of the
pg_table_is_visible builtin function.