{* ../../docs_src/sql_databases/tutorial001_an_py310.py ln[21:22] hl[21:22] *}

### Create a Session Dependency { #create-a-session-dependency }

A **`Session`** is what stores the **objects in memory** and keeps track of any changes needed in the data, then it **uses the `engine`** to communicate with the database.

   * having a hash table of size eight. Providing a large enough estimate at construction time
   * avoids the need for expensive resizing operations later, but setting this value unnecessarily
   * high wastes memory.
   *
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalArgumentException if {@code initialCapacity} is negative
   * @throws IllegalStateException if an initial capacity was already set

      // Another variant of Double Checked Locking.
      //
      // We use two volatile reads. We could reduce this to one by
      // putting our fields into a holder class, but (at least on x86)
      // the extra memory consumption and indirection are more
      // expensive than the extra volatile reads.
      long nanos = expirationNanos;
      long now = System.nanoTime();
      if (nanos == 0 || now - nanos >= 0) {

func (config *TierConfigMgr) getDriver(ctx context.Context, tierName string) (d WarmBackend, err error) {
	config.Lock()
	defer config.Unlock()

	var ok bool
	// Lookup in-memory drivercache
	d, ok = config.drivercache[tierName]
	if ok {
		return d, nil
	}

	// Initialize driver from tier config matching tierName
	t, ok := config.Tiers[tierName]
	if !ok {

    assertThat((long) arraysDim1 * arraysDim2).isNotEqualTo((long) (arraysDim1 * arraysDim2));

    double[][] arrays = new double[arraysDim1][];
    // it's shared to avoid using too much memory in tests
    double[] sharedArray = new double[arraysDim2];
    Arrays.fill(arrays, sharedArray);

    try {
      Doubles.concat(arrays);
      fail();
    } catch (IllegalArgumentException expected) {

	opReadRune2 readOp = 2  // Read rune of size 2.
	opReadRune3 readOp = 3  // Read rune of size 3.
	opReadRune4 readOp = 4  // Read rune of size 4.
)

// ErrTooLarge is passed to panic if memory cannot be allocated to store data in a buffer.
var ErrTooLarge = errors.New("bytes.Buffer: too large")
var errNegativeRead = errors.New("bytes.Buffer: reader returned negative count from Read")

const maxInt = int(^uint(0) >> 1)

    assertThat((long) arraysDim1 * arraysDim2).isNotEqualTo((long) (arraysDim1 * arraysDim2));

    int[][] arrays = new int[arraysDim1][];
    // it's shared to avoid using too much memory in tests
    int[] sharedArray = new int[arraysDim2];
    Arrays.fill(arrays, sharedArray);

    try {
      Ints.concat(arrays);
      fail();
    } catch (IllegalArgumentException expected) {
    }

  }

  @VisibleForTesting
  @WeakOuter
  final class ValueSet extends Sets.ImprovedAbstractSet<V> {
    /*
     * We currently use a fixed load factor of 1.0, a bit higher than normal to reduce memory
     * consumption.
     */

    @ParametricNullness private final K key;
    @VisibleForTesting @Nullable ValueEntry<K, V>[] hashTable;
    private int size = 0;
    private int modCount = 0;

        }
        
        // Verify caching behavior
        assertTrue(file.canCacheWrite());
    }
}
```

## 9. Performance Considerations

### 9.1 Memory Management
- Lease entries should be evicted based on LRU when max leases reached
- Implement periodic cleanup of expired leases

### 9.2 Thread Safety
- Use concurrent data structures for lease storage

// can be disabled via the corresponding `s3HFlag`.
//
// CAUTION: for requests involving large req/resp bodies ensure to pass the
// `traceHdrsS3HFlag`, otherwise both headers and body will be traced, causing
// high memory usage!
func s3APIMiddleware(f http.HandlerFunc, flags ...s3HFlag) http.HandlerFunc {
	// Collect all flags with bitwise-OR and assign operator
	var handlerFlags s3HFlag
	for _, flag := range flags {