Implement an incremental update of the server's local snapshot

[LaurentiuCristofor]

Instead of re-creating the local snapshot multiple times within a transaction, this change enables a single snapshot to be maintained across the entire transaction.

Here are the improvements to the VLR tests:

BEFORE:

349: [value_linked_relationships_parent_only] 10000 records, 3 iterations:
349:    [total]: avg:1499.50ms min:1462.53ms max:1527.97ms
349:   [single]: avg:149.95us min:146.25us max:152.80us


350: [value_linked_relationships_child_only] 10000 records, 3 iterations:
350:    [total]: avg:2946.62ms min:2873.28ms max:3022.14ms
350:   [single]: avg:294.66us min:287.33us max:302.21us


351: [value_linked_relationships_autoconnect_to_same_parent] 5001 records, 3 iterations:
351:    [total]: avg:1388.68ms min:1371.12ms max:1417.48ms
351:   [single]: avg:277.68us min:274.17us max:283.44us


352: [value_linked_relationships_autoconnect_to_different_parent] 10000 records, 3 iterations:
352:    [total]: avg:1458.40ms min:1428.55ms max:1495.40ms
352:   [single]: avg:145.84us min:142.85us max:149.54us

AFTER:

349: [value_linked_relationships_parent_only] 10000 records, 3 iterations:
349:    [total]: avg:499.54ms min:488.44ms max:520.40ms
349:   [single]: avg:49.95us min:48.84us max:52.04us


350: [value_linked_relationships_child_only] 10000 records, 3 iterations:
350:    [total]: avg:919.14ms min:892.11ms max:959.10ms
350:   [single]: avg:91.91us min:89.21us max:95.91us


351: [value_linked_relationships_autoconnect_to_same_parent] 5001 records, 3 iterations:
351:    [total]: avg:902.81ms min:848.74ms max:1004.26ms
351:   [single]: avg:180.53us min:169.72us max:200.81us


352: [value_linked_relationships_autoconnect_to_different_parent] 10000 records, 3 iterations:
352:    [total]: avg:496.94ms min:488.87ms max:510.79ms
352:   [single]: avg:49.69us min:48.89us max:51.08us

[senderista]

Great numbers!

[simone-gaia]

Holy cow! We're getting there :)