cli: add --max-sql-memory flag to cockroach mt start-sql

[jaylim-crl]

Previously the --max-sql-memory flag wasn't available to the multi-tenancy
start-sql command, even though the feature was already there for other
start-related commands.

Release note (cli change): cockroach mt start-sql will now support the
--max-sql-memory flag to configure maximum SQL memory capacity to store
temporary data.

Release justification: The upcoming Serverless MVP release plans to use a
different value for --max-sql-memory instead of the default value of 25%
of container memory. This commit is only a flag change that will only be used
in multi-tenant scenarios, and should have no impact on dedicated customers.

[cockroach-teamcity]

This change is 

[knz]

Given that SQL disk spilling uses pebble, we'll want to enable --cache as well.

Reviewed 1 of 1 files at r1, all commit messages.
Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @andy-kimball and @darinpp)

[jaylim-crl]

TFTR!

Given that SQL disk spilling uses pebble, we'll want to enable --cache as well.

Correct me if I'm wrong, but I think that won't work for a few reasons:

1. The cache size used for DistSQL's temp engine is hardcoded to 128MB:

   cockroach/pkg/storage/temp_engine.go

   Line 72 in 8badea4

   CacheSize(128<<20),

   
   --cache is only used by server.CreateEngines, which isn't used when starting the tenant at all. Looking at old PRs, it looks like the cache size doesn't matter for the temp engine:

   cockroach/pkg/storage/engine/temp_engine.go

   Lines 105 to 107 in 161c2f3

   	// Pebble doesn't currently support 0-size caches, so use a 128MB cache for
   	// now.
   	Cache: cache.New(128 << 20),

2. SQL disk spilling currently does not allow the option of using pebble since we hardcoded the temp storage to use in-memory:

   cockroach/pkg/cli/mt_start_sql.go

   Lines 104 to 110 in 8badea4

   	serverCfg.SQLConfig.TempStorageConfig = base.TempStorageConfigFromEnv(
   	ctx,
   	st,
   	base.StoreSpec{InMemory: true},
   	"", // parentDir
   	tempStorageMaxSizeBytes,
   	)

If we want to enable SQL disk spilling on tenants, we have more work to do, and that should be another PR.

Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @andy-kimball and @darinpp)

[knz]

All right, thanks for explaining.

[knz]

Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @andy-kimball and @darinpp)

[jaylim-crl]

TFTR!

bors r=knz

[craig]

Build succeeded:

• GitHub CI (Cockroach)

[blathers-crl]

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